Adverse effects of Tris. HEPES and MOPS buffers on contractile responses of arterial and venous smooth muscle induced by prostaglandins.

The influence of artificial buffers, Tris, HEPES and MOPS, on PGA1, B2 and F2 alpha-induced contractile responses of isolated rat aorta and portal vein was investigated. All three buffers, in 5mM concentration, when substituted for bicarbonate and phosphate anions, differentially attenuated PG-induced contractile responses; the vein responses exhibited the greater sensitivity to artificial buffer inhibition. In the presence of the artificial buffers, the PG-induced fast phase contractile components on the arterial smooth muscle were obliterated and the slow, tonic components were markedly depressed. PG contractile concentration-effect curves were shifted, differentially, to the right, concomitant with differential reductions in maximum tensions. Reincubation of the vascular tissues in normal Krebs-Ringer bicarbonate for 30-60 min resulted in a complete restoration of full PG-induced contractions. These results support the idea that Tris, HEPES and MOPS may interfere with the binding, translocation and utilization of calcium ions in vascular smooth muscle cells. One must be cautious regarding conclusions drawn for calcium-dependent responses obtained in smooth muscles in which Tris, HEPES or MOPS was the sole buffering agent.