Grosso A, de Sousa R C
Pflugers Arch. 1984 Apr;400(4):349-55. doi: 10.1007/BF00587531.
Substitution of K+ for Na+ in the Ringer solution bathing the inner surface of toad urinary bladders (Bufo marinus) had no effect on basal water permeability but significantly altered the stimulus-hydrosmotic response of this epithelium. In chloride-Ringer, high [K+] increased the hydrosmotic responses to submaximal stimulations induced by vasopressin or exogenous cAMP, while the responses to theophylline or serosal hypertonicity were decreased. In sulfate-Ringer, all these responses were enhanced but for that induced by serosal hypertonicity which was actually diminished. As a step towards determining if Ca2+ might mediate the K+-induced effects on water flow, experiments were conducted either in the presence of a Ca2+ "antagonist" (cobalt) or in nominally Ca2+-free Ringer. In both conditions the hydrosmotic effects of vasopressin and cAMP were markedly reduced. The results raise the possibility that a transient Ca2+ influx through voltage-sensitive, Co2+-blockade Ca2+ channels may play a role in the stimulus-hydrosmotic response of toad urinary bladder.
用K⁺替代浸泡蟾蜍（海蟾蜍）膀胱内表面的林格液中的Na⁺，对基础水通透性无影响，但显著改变了该上皮组织的刺激-渗透反应。在氯化物林格液中，高[K⁺]增加了对血管加压素或外源性cAMP诱导的次最大刺激的渗透反应，而对茶碱或浆膜高渗的反应则降低。在硫酸盐林格液中，所有这些反应均增强，但浆膜高渗诱导的反应实际上减弱。为了确定Ca²⁺是否可能介导K⁺对水流的诱导作用，在存在Ca²⁺“拮抗剂”（钴）或名义上无Ca²⁺的林格液的情况下进行了实验。在这两种情况下，血管加压素和cAMP的渗透作用均明显降低。结果表明，通过电压敏感型Co²⁺阻断Ca²⁺通道的短暂Ca²⁺内流可能在蟾蜍膀胱的刺激-渗透反应中起作用。
