The properties of one ATP-inhibited and one Ca(2+)-dependent K+ channel were investigated by the patch-clamp technique in the soma membrane of leech Retzius neurons in primary culture. Both channels rectify at negative potentials. The ATP-inhibited K+ channel with a mean conductance of 112 pS is reversibly blocked by ATP (Ki = 100 microM), TEA (Ki = 0.8 mM) and 10 mM Ba2+ and irreversibly blocked by 10 nM glibenclamide and 10 microM tolbutamide. It is Ca2+ and voltage independent. Its open state probability (Po) decreases significantly when the pH at the cytoplasmic face of inside-out patches is altered from physiological to acid pH values. The Ca(2+)-dependent K+ channel with a mean conductance of 114 pS shows a bell-shaped Ca2+ dependence of Po with a maximum at pCa 7-8 at the cytoplasmic face of the membrane. The Po is voltage independent at the physiologically relevant V range. Ba2+ (10 MM) reduces the single channel amplitude by around 25% (ATP, TEA, glibenclamide, tolbutamide, and Ba2+ were applied to the cytoplasmic face of the membrane). We conclude that the ATP-dependent K+ channel may play a role in maintaining the membrane potential constant--independently from the energy state of the cell. The Ca(2+)-dependent K+ channel may play a role in generating the resting membrane potential of leech Retzius neurons as it shows maximum activity at the physiological intracellular Ca2+ concentration.

SUMMARY1. Neutral-carrier pH-sensitive microelectrodes were used to investigate intracellular pH (pHi) recovery from alkalinization in leech Retzius neurones in Hepesand in CO2-HC03--buffered solution. The Retzius neurones were alkaline loaded by the addition and subsequent removal of 16 mm acetate, by changing from 5 % C02-27 mM HC03-to 2 % C02-11 mm HCO3-or by changing from C02-HCO3--to Hepes-buffered solution.2. In Hepes-buffered solution (pH 7 4) the mean pHi was 7-29 + 0-11 and the mean membrane potential -44-7 + 5-9 mV (mean + S.D.; n = 83).3. The rate of pHi recovery from alkalinization increased with decreasing pH of the bathing medium (pHb). pHi changed about 0'30 pH units for a pHb unit change. 6. The H+ current blocker Zn2+ (0-5mM) inhibited pHi recovery from alkalinization at resting membrane potential as well as during depolarization. The inhibition was more pronounced during depolarization.7. In Cl--free, C02-HC03--buffered solution pHi recovery from an alkaline load by changing from 5 % C02-27 mm HCO3-to 2 % C02-11 mm HCO3-was slowed by

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We investigated the properties of single K+ channels in the soma membrane of embryonic leech ganglion cells using the patch-clamp technique. We compared these K+ channels with the K+ channels found previously in Retzius neurons of the adult leech. In ganglion cells of 9- to 15-day-old embryos we characterized eight different types of K+ channels with mean conductances of 21, 55, 84, 111, 122, 132, 149 and 223 pS. The 55 pS and 84 pS channels showed flickering and were active for less than 2 min after excising the patch. The 111 pS channel was an outward rectifier, and the open state probability (po) decreased in the inside-out configuration when the Ca2+ concentration was raised from pCa 7 to pCa 3. The 122 pS channel also showed outward rectification. This type of channel was activated after changing from the cell-attached to the inside-out configuration and it did not inactivate during more than 30 min. The po was Ca2+- and voltage-insensitive. One hundred micron glibenclamide reversibly reduced po. The 132 pS channel was an outward rectifier and was Ca2+-insensitive. The 149 pS channel inactivated in the inside-out configuration. The 149- and the 223 pS channel showed inward rectification. The 111 pS channel had similar properties to the Ca2+-dependent K+ channel and the 122 pS channel resembled the ATP-inhibited K+ channel found previously in Retzius neurons of the adult leech.