Lydrup M L, Hellstrand P
Department of Physiology and Biophysics, University of Lund, Sweden.
Pflugers Arch. 1990 Mar;415(6):664-70. doi: 10.1007/BF02584003.
The effects of varying extracellular concentrations of K+ and Ca2+ [K+]o and [Ca2+]o on force development and membrane potential were investigated in the guinea-pig mesotubarium. At [K+]o up to 40 mM, spontaneous action potentials were present, while higher [K+]o gave sustained contractures at a stable membrane potential (-24 to -12 mV for [K+]o from 60 to 120 mM). Tension decreased successively with increasing [K+]o from 30 to 120 mM. The relaxing potency of the dihydropyridine Ca2+ antagonist, felodipine, increased as the membrane was depolarized with increasing [K+]o and action potentials ceased. These results are compatible with the existence of Ca2+ channels showing voltage-dependent affinity with dihydrophyridines. Increasing [Ca2+]o from 2.5 to 10 mM caused membrane hyperpolarization by about 11 mV and was accompanied by a lower frequency of spontaneous contractions and a longer duration of the relaxation between contractions. 86Rb+ efflux measurements in 60 mM K+ in the absence and presence of felodipine revealed a Ca2(+)-dependent component of the voltage-activated efflux. In normal solution (5.9 mM K+), efflux in the presence of felodipine was similar to the minimal value during normal spontaneous activity. The results indicate regulation of the permeability of K+ channels by the intracellular Ca2+ concentration ([Ca2+]i) and suggest participation of such channels in the generation of the regularly occurring bursts of action potentials characteristic of spontaneous activity in the mesotubarium.
在豚鼠中输卵管中研究了细胞外不同浓度的K⁺和Ca²⁺（[K⁺]o和[Ca²⁺]o）对力产生和膜电位的影响。在[K⁺]o高达40 mM时，存在自发动作电位，而更高的[K⁺]o在稳定的膜电位下（对于[K⁺]o从60到120 mM，膜电位为-24至-12 mV）产生持续挛缩。随着[K⁺]o从30 mM增加到120 mM，张力依次降低。随着膜因[K⁺]o增加而 depolarized 且动作电位停止，二氢吡啶Ca²⁺拮抗剂非洛地平的舒张效力增加。这些结果与存在对二氢吡啶具有电压依赖性亲和力的Ca²⁺通道一致。将[Ca²⁺]o从2.5 mM增加到10 mM导致膜超极化约11 mV，并伴有自发收缩频率降低和收缩之间舒张持续时间延长。在不存在和存在非洛地平的情况下，在60 mM K⁺中进行的⁸⁶Rb⁺外流测量揭示了电压激活外流的Ca²⁺依赖性成分。在正常溶液（5.9 mM K⁺）中，非洛地平存在时的外流类似于正常自发活动期间的最小值。结果表明细胞内Ca²⁺浓度（[Ca²⁺]i）对K⁺通道通透性的调节，并提示此类通道参与中输卵管自发活动特征性的规律性动作电位爆发的产生。
