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Long Ca 2+ channel opening induced by large depolarization and Bay K 8644 in smooth muscle cells isolated from guinea‐pig detrusor
Author(s) -
Nakayama S.,
Brading Alison F.
Publication year - 1996
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1996.tb15731.x
Subject(s) - depolarization , pipette , biophysics , chemistry , patch clamp , guinea pig , conductance , electrophysiology , membrane potential , anatomy , neuroscience , medicine , biology , physics , condensed matter physics
1 In smooth muscle cells enzymatically isolated from guinea‐pig urinary bladder, Ca 2+ channel currents were recorded by conventional cell‐attached patch clamp techniques. In most recordings Bay K 8644 (2 μ m ) was contained in the patch pipette. 2 Closure of Ca 2+ channels observed during the repolarizing steps was significantly slowed by preconditioning with large depolarizations (+80 and 100 mV), with or without Bay K 8644 in the pipette. 3 The sum of the unitary Ca 2+ channel current traces obtained after large conditioning depolarizations (in the presence of Bay K 8644) showed a slowly deactivating tail current. 4 By use of this slow deactivating feature, the current‐voltage relationship of the unitary Ca 2+ channel current was continuously measured with a ramp pulse after large depolarization. The slope conductance ranged from 22 to 30 pS, compatible with that of L‐type Ca 2+ channels. 5 It is concluded that L‐type Ca 2+ channels in guinea‐pig detrusor cells are open for much longer after large depolarizations consistent with their being two channel open states, and that Bay K 8644 prolongs the lifetime of both open states. The underlying mechanisms are discussed.