Clinically relevant concentrations of ethanol modulate the function of a number of ion channel proteins. A fundamental question regarding the effects of alcohol is whether the drug modifies ion channels by directly binding to the protein, indirectly by perturbing the surrounding membrane lipid, or some combination of both. This thesis further characterized ethanol's site of action by examining the effects of ethanol on N-methyl-D-aspartate (NMDA) receptor/channels and large conductance Ca2+-activated K+ (BK) channels at a number of levels using direct electrophysiological methods. In Chapter One, the magnitude of ethanol's inhibition of a number of cloned heteromeric NMDA receptor/channels in the absence or presence of a number of modulators was compared. The rank order of ethanol sensitivity for the subunit combinations studied was NR1b/NR2A > NR1b/NR2B > NR1b/NR2C > NR1b/NR2D. Modulation of the receptor with Mg2+, Zn2+, the glycine antagonist 7-Chlorokynurenic Acid, or after reduction or oxidation of the redox regulatory site did not alter the ethanol sensitivity of heteromeric NMDA receptors. Therefore, the ethanol sensitivity of NMDA receptor/channels is dependent upon which NR2 subunit is present, and ethanol's site of action is unrelated to these modulatory sites on the receptor/channel protein. In Chapter Two, ethanol's site of action at cloned BK channels was characterized using of a number of 1-alkanols. Ethanol, butanol, hexanol, and heptanol reversibly and dose-dependently increased the current carried through BK channels. Longer chain 1-alkanols, such as octanol had no effect on channels. In Chapter Three, the action of ethanol on BK channels reconstituted in a number of model planar bilayers was studied. Ethanol increased the activity of BK channels incorporated in bilayers composed of phosphatidylethanolamine (PE) and phosphatidylserine (PS) or PE alone by decreasing the average amount of time channels dwelled in the closed state. There was no significant effect of alcohol on either channel conductance or unitary current. Taken together, these data suggest that ethanol action on BK channels does not require the complex membrane architecture found in native membranes, and does not require freely diffusible cytoplasmic factors or proteins.

We examined the actions of ethanol on the single channel properties of large conductance Ca2+-activated K+ (BK) channels isolated from skeletal muscle T-tubule membranes and incorporated into planar lipid bilayer membranes. We have taken advantage of this preparation, because it lacks most elements of cellular complexity, including cytoplasmic constituents and complex membrane lipid composition and architecture, to examine the minimum requirements for the effects of alcohol. Clinically relevant concentrations (25-200 mM) of ethanol increased the activity of BK channels incorporated into bilayers composed of phosphatidylethanolamine (PE) alone or PE and phosphatidylserine. The potentiation of channel activity by ethanol was attributable predominantly to a decrease in the average amount of time spent in closed states. Ethanol did not significantly affect the current amplitude-voltage relationship for BK channels, indicating that channel conductance for K+ was unaffected by the drug. Although base-line characteristics of BK channels incorporated into bilayers composed only of PE differed from those of channels in PE/ phosphatidylserine in a manner expected from the change in bilayer charges, the actions of ethanol on channel activity were qualitatively similar in the different lipid environments. The effects of ethanol on single channel properties of BK channels in the planar bilayer are very similar to those reported for the action of ethanol on neurohypophysial BK channels studied in native membrane, and for cloned BK channels expressed in Xenopus laevis oocytes, which suggests that ethanol's site and mechanism of action are preserved in this greatly simplified preparation.

BACKGROUND: Partial liquid ventilation with perfluorocarbon is a new therapeutic strategy to treat various lung disorders. The current study was undertaken to determine the efficacy of partial liquid ventilation with a perfluorocarbon (FC-77) in the treatment of pneumococcal pneumonia in rats. METHODS: Male Wistar rats (weight, 275-300 g; n, 75) were infected via direct intratracheal inoculation with ca 10(9) colony-forming units of viable Streptococcus pneumoniae, serotype 3, and 24 h after infection were placed into one of five groups, each containing 15 rats. The groups were (1) no treatment, (2) one intramuscular injection of penicillin G benzathine (200,000 U), (3) partial liquid ventilation with FC-77, (4) partial liquid ventilation with FC-77 and a single intramuscular dose of penicillin G benzathine (200,000 U), and (5) gas ventilation. Animals were observed every 24 h for survival. RESULTS: All untreated or gas-ventilated animals or animals that received only partial liquid ventilation were dead by 7 days. Those receiving only partial liquid ventilation survived longer than untreated controls, but ultimately all succumbed by day 7. Survival was 40% for penicillin-treated rats compared with controls (P < 0.05) and 80% for animals treated with both partial liquid ventilation and penicillin versus antibiotic alone (P < 0.05). CONCLUSIONS: These observations suggest that partial liquid ventilation with perfluorocarbon in combination with antibiotic administration may be an effective therapeutic modality in pneumococcal pneumonia.

It is not known whether alcohols modulate ion channels by directly binding to the channel protein or by perturbing the surrounding membrane lipid. Cutoff describes the phenomenon where the potency of 1-alkanols monotonically increases with alkyl chain length until a loss of efficacy occurs. Determination of the cutoff for a variety of channels can be important, because similar and/or dissimilar cutoffs might yield information regarding the nature of ethanol's site of action. In this study, the two-electrode voltage clamp technique was used to determine the cutoffs for the 1-alkanol potentiation of cloned Ca(2+)-activated-K+ (BK) channels and for the inhibition of cloned Shaw2 K+ channels, expressed in Xenopus oocytes. Ethanol, butanol, hexanol, and heptanol reversibly enhanced BK currents, whereas octanol and nonanol had no effect. In contrast, Shaw2 currents were potently inhibited by both octanol and decanol, but not by undecanol. Taken together, data demonstrate that the modulation of K+ channels by long chain alcohols is channel-specific. Interestingly, ethanol was a less potent activator of BK currents in the intact oocyte in comparison with its effect on this channel in excised membrane patches. The decrease in potency could not be attributed to an ethanol-dependent change in Ca2+ influx through endogenous voltage-gated channels, an effect that would alter the concentration of Ca2+ available to activate BK channels.

The NMDA receptor/channel has been shown to be inhibited by ethanol in the clinically relevant range 25-100 mM. We studied heteromeric assemblies (NR1b/NR2) of the NMDA receptor, expressed in oocytes, to address three questions regarding this inhibition, and discovered the following: (1) The inhibition was nearly equivalent when ethanol was coapplied with the agonist, and when ethanol was introduced after steady-state current was established, suggesting that ethanol does not act by interfering with the activation process of the NMDA receptor. (2) The degree of inhibition was controlled by the NR2 subunit, with both NR2A and NR2B significantly more sensitive to ethanol than NR2C and NR2D. (3) Manipulation of the NMDA receptor with a number of agents that normally modulate it did not alter the degree of inhibition produced by ethanol. The presence of Mg2+ (3 and 12.5 microM), Zn2+ (1 and 10 microM), or the glycine antagonist 7-chlorokynurenic acid (1.25 or 5 microM), did not alter the ethanol sensitivity of heteromeric (NR1b/NR2A, NR1b/NR2B, NR1b/NR2C) NMDA receptors. Redox modulation of the NMDA receptor by dithiothreitol (2 mM) or 5,5'-dithiobis(2-nitrobenzoic acid) (1 mM) also did not alter the degree to which ethanol inhibits NMDA receptors. Taken together, these results indicate that the ethanol sensitivity of native NMDA receptors, which likely exist in heteromeric form, results from actions at a site different from those of known modulators of the receptor.