Calcium dependence of ouabain-induced contraction in aortas from spontaneously hypertensive rats.
The calcium sensitivity of ouabain-induced contractions of aortic strips from spontaneously hypertensive rat (SHR) was examined using several drugs which affect Na+ and Ca2+ movements across the cell membrane, and the results were compared with those obtained with age-matched Wistar-Kyoto rat (WKY). The Ca2+ concentration-response curves (10(-3) M ouabain-treated preparations) made with aortic strips from SHR lay to the left of those made with aortic strips from WKY (Ca EC50 values: SHR, 0.51 +/- 0.16 mM, n = 6; WKY, 1.23 +/- 0.41 mM, n = 7; P less than 0.05). Amiloride (a Na+ entry blocker) and nifedipine (a Ca2+ entry blocker) attenuated the sensitivity to Ca2+ of SHR and WKY aortic strips. With 2 x 10(-4) M amiloride, WKY vessels showed a 1.3-fold increase in the Ca EC50 value and SHR a 2.1-fold increase. With 10(-6) M nifedipine. WKY vessels showed a 1.1-fold increase in the Ca EC50 value and SHR a 1.5-fold increase. Addition of monensin (Na ionophore) produced a dose-dependent potentiation in ouabain-treated aorta from WKY, but not in ouabain-treated aorta from SHR. Addition of 1.5 x 10(-5) M A23187 (Ca ionophore) eliminated the difference between the Ca2(+)-induced contractions in aortas from SHR and WKY. These results suggest that enhancement of Ca2+ influx by Na(+)-Ca2+ exchange and/or voltage-dependent Ca2+ channels in vascular smooth muscle cell membranes may be an important factor in the difference between ouabain-induced contractions in aorta from SHR and WKY.
Shibata
R
R
1st Department of Internal Medicine, Hyogo College of Medicine, Japan.
Morita
S
S
Nagai
K
K
Miyata
S
S
Iwasaki
T
T
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D066298:In Vitro Techniques; D008985:Monensin / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology
D002121:Calcium Channel Blockers; D000001:Calcimycin; D010042:Ouabain; D008985:Monensin; D012964:Sodium; D004110:Diltiazem; D011188:Potassium; D002118:Calcium