Abstract
The effect of caffeine on contractile activity and Ca movement was investigated in guinuEa pig taenia coll. Caffeine at a concentration of 7 mM produced a contraction for approx. 7 min and increased 45Ca influx and efflux without a change in Ca content in the tissue. The effect of caffeine on Ca movement was the same as that of carbachol in the early phase of the contractile response. The caffeine-contraction was not potentiated by an addition of Ca up to four times that of normal concentration, however, the carbachol-contraction was potentiated. When the muscle was soaked in a Ca-free solution, it showed “Ca-free contraction” and a loss of the tissue Ca content. When caffeine was added immediately after the “Ca-free contraction” was relaxed, caffeine produced a transient contraction and increased the loss of the tissue Ca content. Under identical circumstances, carbachol did not induce a contraction or affect the Ca content of the tissue. In conclusion, caffeine was demonstrated to increase Ca exchangeability in smooth muscle cell as did carbachol, however, the results suggested the possibility that caffeine releases a bound Ca in the cell for contraction whereas carbachol induces a contraction by an increase in a permeability of the cell membrane to Ca ions.
