A SHIFT OF CELLULAR CALCIUM TO A MORE SLOWLY EXCHANGEABLE FRACTION DURING CONTRACTION IN GUINEA PIG TAENIA COLI

[摘要] References(27)Cited-By(8)It is now generally agreed that Ca ion is essential for the contraction of smooth muscle. On the role of Ca ion in the contraction cycle of smooth muscle, many electrophysiological studies have suggested that the action potential of the muscle cell is associated with an inward movement of Ca ions from anionic sites of cell membrane or from extracellular space and this Ca flow may initiate contractile response (1, 2). It has also been suggested from radioisotope studies (3-6) that contraction in smooth muscle may be triggered and maintained by release of cellular Ca and/or by influx of extracelluar Ca. Although Ca ions activating contractile protein of smooth muscle are said to be inactivated and stored in the cell until expelled (7), the mechanism is still obscure. In previous experiments, tissue Ca of taenia coli was tentatively divided into two fractions; a fraction which exchanges within 4 min and another fraction which is exchangeable but does not exchange within 4 min, the latter more slowly exchangeable fraction was named as “tightly bound fraction”(TBF) (4). The size of TBF increased during tonic contraction induced by carbachol, pilocarpine (3), histamine (4), barium (5) and 40 mM potassium (5, 6), and decreased during abolition of tension by specific antagonists oft he stimulants (3, 4), metabolic inhibiting factors and factors inhibiting active Na transport (8, 9). from these data., it was suggested that the increase in the size of TBF, i.e., a shift of cellular Ca to a more slowly exchangeable fraction, could be related to contraction of smooth muscle, and the movement of Ca related to metabolism. In the experiment reported here, the effect of external phosphate on the slowly exchanging Ca fraction, the change in the fraction in the course of muscle contraction and relaxation and exchange kinetics of the fraction were studied to clarify the nature of the shift of cellular Ca to a more slowly exchanging fraction in smooth muscle of taenia coil and the role of this Ca movement in excitation-contraction coupling in smooth muscle.

[学科分类] 药理学