Effects of K-free solution on tension development and Na content in vascular smooth muscles isolated from guinea-pig, rat and rabbit

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Abstract
The effects of K-free solution on tension development and cellular Na content were investigated in aortic strips isolated from guinea-pig, rat and rabbit and in rabbit ear artery. Experiments were conducted in the presence of phentolamine (5×10−7 to 10−6 M) in order to eliminate the possible influence of endogenous catecholamine. K-free solution produced contractions and increased cellular Na content in these vascular smooth muscle preparations. The rate of increase in K-free contraction of rabbit aorta and ear artery was much slower than that of guinea-pig and rat aortae. The rate of accumulation of Na in rabbit arterial smooth muscle preparations was also much slower than that in guinea-pig and rat aortae. When the relationship between tension development and cellular Na content was compared in these arteries, it was found that an increase in cellular Na produced a greater increase in tension in guinea-pig and rat aortae than in rabbit aorta and ear artery. It is suggested that the slow and small responses of rabbit arterial smooth muscles to K-free solution might be due to a slow accumulation of Na and to a smaller role of transmembrane Na gradient in the regulation of cellular Ca.