title: Calcium-sensitivity of the plasmalemmal delayed rectifier potassium current suggests that calcium influx in pulvinar protoplasts from Mimosa pudica L. can be revealed by hyperpolarization.
abstract: Isolated protoplasts from pulvinar motor cells of Mimosa pudica were studied using conventional whole-cell patch clamp techniques. With internal solutions weakly buffered for Ca2+ (0.2 mM EGTA), a rundown of the outward delayed rectifier K+ current was induced by hyperpolarizing the holding potential, and this effect was strongly promoted by high external Ca2+ concentrations. This rundown could be reversed by coming back to less hyperpolarized holding potentials or by lowering the external [Ca2+]. Such rundown was absent when pipette internal solutions strongly buffered (10 mM EGTA) for Ca2+ were used. Ionomycin induced rundown of the K+ current with internal solutions containing 0.2 mM but not 10 mM EGTA. The hyperpolarization-associated rundown was reversibly blocked by Gd3+ and La3+.
mesh_terms: D015764:Bepridil / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers; D002478:Cells, Cultured; D004553:Electric Conductivity; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D009568:Nitrendipine / Q000494:pharmacology; D018521:Plant Physiological Phenomena; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011523:Protoplasts; D018516:Pulvinus / Q000166:cytology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D007476:Ionophores; D015221:Potassium Channels; D015759:Ionomycin; D015764:Bepridil; D009568:Nitrendipine; D014700:Verapamil; D002118:Calcium