The electrophysiological properties of the cell membrane of rat spermatogenic cells were studied using the whole‐cell variation of the patch‐electrode voltage‐clamp technique. In late primary spermatocytes and early spermatids isolated from adult testis, a transient inward current followed by a slowly developing outward current was produced when the membrane potential was made more positive than ‐60 mV. Early spermatogenic cells which consist of spermatogonia and early spermatocytes were isolated either from new‐born rats (12‐14 days old) of from adult cryptorchid rats 15‐21 days after the operation. In early spermatogenic cells, some showed a slowly developing outward current with negligible initial inward current, while others showed a recognizable inward current followed by the slowly developing outward current. The inward currents are identified as Ca2+‐carried current, since replacement of external Ca2+ with Mn2+ reversibly diminished the current whereas Ba2+ or Sr2+ substituted for Ca2+. The reversal potential of the outward current changed from ‐65 to ‐12 mV when [K+]o was raised from 5 to 100 mM. The outward current was independent of [Ca2+]o and was blocked by tetraethylammonium chloride. Thus the current was identified as membrane‐potential‐dependent K+ current. During spermatogenesis from spermatogonia to early spermatids, the density of Ca2+ current increased while the K+ current density decreased significantly.
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