Study on double reciprocal innervation of the iris dilator muscle and sphincter muscle by a whole cell patch-clump technique

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It is well-known that both the iris dilator muscle and the sphincter muscle are innervated doublely by the sympathetic and parasympathetic nerves by recent research applied the histochemical, pharmacological, physiological techniques. The purpose of this study is to investigate the double reciprocal innervation of the iris muscle cells, the dilator and the sphincter muscle by means of a whole cell patch-clump technique. Preceding the study we cultured the dilator and the sphincter cells to get considerable amonuts of the homogenous materials. Proof of the muscle cells was done with immunohistochemical method. The surface of the cultured cells was rather flat and the membrane was fragile. Although they were not fully suitable for the experiment, we recorded the resting membrane potential in the selected cells. It was found to be low, 0 to-5 mV.The action potential could not be record by the electrical stimulation. According to Watanabe et al (1) neither nerve nor direct electrical stimulation with short pulses of the sphincter nuscle elicited any changes in the membrane potential under physiological conditions. It belongs to a low-excitability smooth muscle such as the trachea, aorta and pulmonary artery. Our results appears to support their conclusion. The low-excitability of the muscle is due to the balance between the inward current (Ca^<2+> current) and the outward current (K^+ current) elicited by depolarization (4,5). Diversity of membrane excitability in smooth muscle has become recently known. The nature of the iris smooth muscles is quite different from what we previously assumed. We plan first to develop our theme for the investigation of Ca^<2+> current of the iris muscle cell membrane. Concerning the dilator muscle, as far as we know , there is no report on patch-clump technique.