Intracellular and extracellular calcium utilization during hypoxic vasoconstriction of cyclostome aortas

Hypoxic vasoconstriction (HV) is an intrinsic response of mammalian pulmona ry and cyclostome aortic vascular smooth muscle. The present study examined the utilization of calcium during HV in dorsal aortas (DA) from sea lampre y and New Zealand hagfish. HV was temporally correlated with increased free cytosolic calcium (Ca-c(2+)) in lamprey DA. Extracellular calcium (Ca-o(2)) did not contribute significantly to HV in lamprey DA, but it accounted f or 38.1 +/- 5.3% of HV in hagfish DA. Treatment of lamprey DA with ionomyci n, ryanodine, or caffeine added to thapsigargin-reduced HV, whereas HV was augmented by BAY K 8644. Methoxyverapamil (D600) in zero Ca-o(2+) did not a ffect HV in lamprey DA, nor did it prevent further constriction when Ca-o(2 +) was restored during hypoxia in hagfish DA. Removal of extracellular sodi um (Na-o(+)) caused a constriction in both species. Lamprey DA relaxed to p rehypoxic tension following return to normoxia in zero Na-o(+), whereas rel axation was inhibited in hagfish DA. Relaxation following HV was inhibited in lamprey DA when Na-o(+) and Ca-o(2+) were removed. These results show th at HV is correlated with [Ca2+](c) in lamprey DA and that Na+/Ca2+ exchange is used during HV in hagfish but not lamprey DA. Multiple receptor types a ppear to mediate stored intracellular calcium release in lamprey DA, and L- type calcium channels do not contribute significantly to constriction in ei ther cyclostome.