GAP JUNCTION FUNCTION IN VASCULAR SMOOTH-MUSCLE - INFLUENCE OF SEROTONIN

In this study we examined the effects of serotonin (5-hydroxytryptamin e, 5-HT) on the function of gap junctions between smooth muscle cells isolated from human and pig coronary and rat mesentery arteries and be tween A7r5 cells (cell line derived from embryonic rat aorta). Mesente ry and pig coronary cells expressed connexin (Cx) 43, and human corona ry cells expressed Cx40. Mesentery and pig coronary cells each exhibit ed a single gap junction channel population with unitary conductances of 75 and 59 pS, respectively. Human coronary cells exhibited two chan nel populations with unitary conductances of 51 and 107 pS. The A7r5 c ells express Cx40 and Cx43 and exhibit three channel populations with unitary conductances of 70, 108, and 141 pS. Under control conditions, junctional conductance between the four cell types ranged from 11 to 20 nS. During maximal stimulation with 5-HT (1-10 mu M), junctional co nductance increased (29-75%) in all four cell types. The unitary condu ctance profiles in the rat mesentery and pig coronary cells were unaff ected by 5-HT, suggesting that the observed increase in macroscopic co nductance reflects an increase in open probability. Unitary conductanc es were also unaffected in the human coronary and A7r5 cells. However, there was a reduced frequency of the 105-pS channel in the human coro nary cells and of the 70- and 141-pS channels in the A7r5 cells. These changes in the relative frequency histograms suggest that the open pr obabilities of the various channel types are differentially affected b y the 5-HT treatment. Thus the data suggest that vascular smooth muscl e cells exhibit a variety of channel types whose open probabilities ar e differentially affected by 5-HT stimulation.