Gap junctions in isolated rat aorta: evidence for contractile responses that exhibit a differential dependence on intercellular communication

Connexin43 (Cx43) is a major gap junction protein present in the Fischer-344 rat aorta. Previous studies have identified conditions under which selective disruption of intercellular communication with heptanol caused a significant, readily reversible and time-dependent diminution in the magnitude of alpha(1)-adrenergic contractions in isolated rat aorta. These observations have indentified a significant role for gap junctions in modulating vascular smooth muscle tone. The goal of these steady-state studies was to utilize isolated rat aortic rings to further evaluate the contribution of intercellular junctions to contractions elicited by cellular activation in response to several other vascular spasmogens. The effects of heptanol were examined (0.2-2.0 mM) on equivalent submaximal (approximate to 75% of the phenylephrine maximum) aortic contractions elicited by 5-hydroxykyptamine (5-HT; 1-2 mu M), prostaglandin F-2 alpha (PGF(2 alpha); 1 mu M) and endothelin-1 (ET-1; 20 nM). Statistical analysis revealed that 200 mu M and 500 mu M heptanol diminished the maximal amplitude of the steady-state contractile responses for 5-HT from a control response of 75 +/- 6% (N = 26 rings) to 57 +/- 7% (N = 26 rings) and 34.9 +/- 6% (N = 13 rings), respectively (P<0.05), and for PGF(2 alpha) from a control response of 75 +/- 10% (N = 16 rings) to 52 +/- 8% (N = 19 rings) and 25.9 +/- 6% (N = 18 rings), respectively (P<0.05). In contrast, 200 mu M and 500 mu M heptanol had no detectable effect on the magnitude of ET-1-induced contractile responses, which were 76 +/- 5.0% for the control response (N = 38 rings), 59 +/- 6.0% in the presence of 200 mu M heptanol (N = 17 rings), and 70 +/- 6.0% in the presence of 500 mu M heptanol (N = 23 rings) (P<0.13). Increasing the heptanol concentration to 1 mM was associated with a significant decrease in the magnitude of the steady-state ET-1-induced contractile response to 32 +/- 5% (21 rings; P<0.01); further increasing the heptanol concentration to 2 mM had no additional effect. In rat aorta then, junctional modulation of tissue contractility appears to be agonist-dependent.