Wilde D W, Marshall J M
Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912.
Biol Reprod. 1988 May;38(4):836-45. doi: 10.1095/biolreprod38.4.836.
In the pregnant rat, spontaneous electrical activity of circular muscle (CM) changes from single, plateau-type action potentials at early and mid-term to repetitive spike trains at term. To examine mechanisms underlying the plateau, we studied the effects of potassium channel blockers tetraethylammonium (TEA) and 4-aminopyridine (4-AP) on membrane potentials in CM from rats on gestation Days 14, 15, 16, 21 (term). Apparent membrane conductance was measured at rest and during the plateau in Day 14 muscles with and without TEA. 4-AP depolarized the resting membrane on all gestation days. Therefore, a direct action of 4-AP on plateau configuration could not be separated from an indirect effect of depolarization. TEA did not affect the resting potential but increased action potential size and depolarization rate on all gestation days. On Day 16, TEA reduced plateau amplitude, unmasking small, repetitive depolarizations. D-600 decreased plateau amplitude and duration and attenuated these effects of TEA. Plateau conductance increased initially then decreased before membrane repolarization. Membrane conductance and outward rectification during the plateau were reduced by TEA. The plateau potential may result from an outwardly rectifying TEA-sensitive current combined with a slow inward current, the plateau magnitude being determined by the relative intensity of each current.
在妊娠大鼠中，环行肌（CM）的自发电活动从妊娠早期和中期的单个平台型动作电位转变为足月时的重复尖峰序列。为了研究平台电位的潜在机制，我们研究了钾通道阻滞剂四乙铵（TEA）和4-氨基吡啶（4-AP）对妊娠第14、15、16、21天（足月）大鼠CM膜电位的影响。在有或没有TEA的情况下，测量第14天肌肉静息时和平台期的表观膜电导。4-AP使所有妊娠天数的静息膜电位去极化。因此，4-AP对平台电位构型的直接作用无法与去极化的间接作用区分开来。TEA不影响静息电位，但在所有妊娠天数均增加动作电位大小和去极化速率。在第16天，TEA降低了平台电位幅度，揭示了小的重复去极化。D-600降低了平台电位幅度和持续时间，并减弱了TEA的这些作用。平台期电导在膜复极化前先增加后降低。TEA降低了平台期的膜电导和外向整流。平台电位可能由外向整流的TEA敏感电流与缓慢内向电流共同产生，平台电位大小由每种电流的相对强度决定。
