[Effect of potassium ions on electrogenesis and contraction of ureter smooth muscle].
In the ureter smooth muscle cells, high--K solution produced a depolarization at the onset of which the action potentials (AP) and contraction occur; the latter consists of an initial phasic (Ph) and subsequent tonic (T) components. Ph component is initiated by the AP, T component--by a stable potassium depolarization. In Ca--free solution the AP, Ph and T components are blocked, although a sustained potassium depolarization is preserved. Basing on these results it is suggested that: 1) phasic contraction is initiated by calcium ions influxed via fast potential--dependent calcium channels participating in the AP generation; 2) tonic contraction is also initiated mainly by extracellular calcium influx through slow potential--dependent calcium channels of plasmatic membrane that appear to be similar to calcium channels of sarcoplasmic reticulum membrane in skeletal muscles and of the membrane of presinaptic nerve terminals.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D011188:Potassium / Q000494:pharmacology*; D014513:Ureter / Q000187:drug effects*
D007473:Ion Channels; D011188:Potassium; D002118:Calcium
Deĭstvie ionov kaliia na élektrogenez i sokrashchenie v gladkikh myshtsakh mochetochnika.