THE RELATIONSHIP OF KCL-MEDIATED AND PROSTAGLANDIN F-2-ALPHA-MEDIATED INCREASES IN TENSION OF THE PORCINE CORONARY-ARTERY WITH CHANGES IN INTRACELLULAR CA-2+ MEASURED WITH FURA-2

1 Changes in intracellular free Ca2+ concentration ([Ca2+]i) were measured simultaneously with changes in muscle tension by use of the fluorescent Ca2+ indicator, fura-2, in coronary arterial rings of the pig. 2 Changes in [Ca2+]i were measured by monitoring the ratio of fluorescence due to excitation at 340 nm (F340) to that at 380 nm (F380). 3 Increases in tension of the porcine coronary artery induced by prostaglandin F2-alpha (PGF2-alpha) (2-30-mu-M) and KCl (25-70 mM) were accompanied by increases in the F340/F380 fluorescence ratio of fura-2. 4 KCl-induced increases in muscle tension, equivalent to those produced by PGF2-alpha, were observed to occur in the presence of a higher [Ca2+]i. 5 Nearly complete relaxation of KCl-induced contractions by sodium nitroprusside (SNP) was accompanied by only a partial reversal of the increase in [Ca2+]i that occurred during contraction. 6 Complete relaxation of the PGF2-alpha-contracted coronary artery by cromakalim (BRL 34915) was accompanied by a nearly complete reversal of the increase in [Ca2+]i caused by the contractile agent. 7 The contractile state of smooth muscle is not an indicator of [Ca2+]i. The [Ca2+]i-tension relationship is dependent upon the type of pharmacological agent that is used to change muscle tension.