| Abstract: | The purpose of these experiments was to study the temporal relationship between tension development in incubated guinea pig tracheal smooth muscle and changes in tissue levels of cAMP and cGMP, and isotopic Ca. Dose-response studies were performed with increasing concentrations of histamine both in the absence and presence of H1 receptor blockade using 10(-5) M diphenhydramine. The time course of tension development was subsequently determined in the presence of three concentrations of histamine shown to cause 50% (3 X 10(-6) M), 85% (9 X 10(-6) M), and 100% (5 X 10(-5) M) of maximal contraction. Tissue cyclic nucleotide and 45Ca levels were measured 20 sec, 1 min, and 6 min after the onset of contraction. For comparison, the influence of carbachol was also studied. Our findings demonstrate that there were no detectable alterations in tissue cAMP or cGMP levels during the initial phases of contractile change. In contrast, tissue isotopic Ca uptake increased early in histamine-induced contraction and was blocked by the H1 antagonist. |
