Aortic responses to vanadate: independence from (Na,K)-ATPase and comparison of Dahl salt-sensitive and salt-resistant rats.

Abstract

SUMMARY Vanadate at doses from 10"" to 10~* M caused a dose-dependent contraction of the rat aorta in vitro. Aortas of Dahl salt-hypertension sensitive (S) rats responded to ranadate with a greater contraction than Dahl salt-hypertension resistant (R) rats. In contrast, S and R aortic responses to depolarization with potassium were equal, and responses to norepinephrine were less in S than R. The mechanism by which vanadate causes the aortic response was studied in S rats. In aortic smooth muscle sodium-loaded by exposure to low potassium media followed by a norepinephrine-induced contraction, a relaxation induced with 5 mM potassium was not influenced by 10' M vanadate. Since this potassium-induced relaxation is known to be a reflection of (Na,K)-ATPase activity, these data snow that vanadate (up to 10"' M) does not inhibit (Na,K)-ATPase in intact smooth muscle cells although it is a known potent inhibitor of (Na, 1 ' 2 It has been argued that inhibition of (Na,K)-ATPase in vascular smooth muscle could result in contraction of the muscle.'-4 Our primary goal was to determine if vanadate caused a response in vascular smooth muscle in vitro, and, if so, whether this response was related to inhibition of the (Na,K)-ATPase pump. Second, we compared aortic responses to vanadate in rats selectively bred by Dahl et al.KB for sensitivity (S strain) or resistance (R strain) to the hypertensive effect of high salt diet. Materials and MethodsSalt-sensitive (S) and salt-resistant (R) rats were bred in our laboratory from stock originally obtained from Dahl in 1972. Rats were fed normal laboratory rat chow that contained 1% NaCl. Blood pressure was obtained by the tail microphonic method* with the rats under ether anesthesia.Rats were killed by cervical dislocation. The thoracic aorta was removed, placed in ice cold medium (see below), and dissected free of fat. Rings (5 mm long, measured against a steel ruler) were cut from the thoracic aorta just above the diaphragm and mounted on stainless steel hangers in a muscle bath at 37°C under 2 g of tension. Muscles were allowed to equilibrate 1 hour before use. The medium contained 118 mM NaCl, 4.7 mK KC1, 12.5 mM NaHCO,, 1.2 mM KH,PO 4 , 1.2 mM MgSO 4 , 2.5 mM CaCl,, 11.1 mM glucose, and was gassed with 95% O a , 5% CO,, pH 7.3. Tension was recorded using a Grass Instrument (Quincy, Massachusetts) FT.03 force displacement transducer and a Grass Model 79 polygraph. At the end of experiments, aortic rings were blotted to remove excess media and weighed on a Cohn microbalance. Injections into the muscle chamber were made using microliter syringes. Sodium orthovanadate (Na a VO 4 ) (Fisher) was added as a 0.1 M solution to yield the concentrations indicated. Ouabain, (-)-norepinephrine and 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS) were obtained from Sigma. Phentolamine was a gift from Ciba.From the

Effects of soldium vanadate on the smooth muscle of the guinea-pig vas deferens.

“…Sodium vanadate also caused tension development in the presence of high concentration of ouabain, as has been reported in vascular smooth muscles (Ozaki & Urakawa, 1979 ;Hudgins & Bond, 1981;Rapp, 1981). Moreover, it has been reported that even though vanadate is taken into vascular smooth muscle cells, there is no inhibition of Na, K-ATPase (Searle et al, 1983).…”

“…In smooth muscles, little is known regarding the action of vanadate (Huot et al, 1979;Ozaki & Urakawa, 1980;Garcia et al, 1981;Hudgins & Bond, 1981;Rapp, 1981;Ueda et al, 1982;Nayler & Sparrow, 1983). These reports of the action of vanadate on smooth muscles are in agreement in that vanadate acts directly on smooth muscle and causes contraction.…”

“…These reports of the action of vanadate on smooth muscles are in agreement in that vanadate acts directly on smooth muscle and causes contraction. In vascular, intestinal and air-way smooth muscles, it has been thought that the stimulating action of vanadate is not mediated by inhibition of Na, K-ATPase (Ozaki & Urakawa, 1980;Hudgins & Bond, 1981;Rapp, 1981;Nayler & Sparrow, 1983).…”

Dahl salt-susceptible and salt-resistant rats. A review.

“…104 Aortic rings from S rats do, however, respond with a greater contraction than those from R in response to vanadate anion. 105 Although vanadate is a known potent inhibitor of Na + ,K + -ATPase in vitro, it can be shown that: 1) the contraction of the aortic rings by vanadate is not due to inhibition of the Na + ,K + -pump activity; and 2) vanadate action is blocked by a specific inhibitor of anion transport, suggesting that vanadate works from inside the cell. In these experiments, aortic rings from the two strains contracted similarly to depolarizing concentrations of K + , and S contracted with less force than R in response to norepinephrine.…”

Effects of vanadate on mechanical and electrical activities in guinea-pig taenia coli.

“…(Borchard et al, 1979;Erdmann et al, 1979). It was also found that VAN produces contraction in isolated vascular smooth muscle (Hout et al, 1979;Rapp, 1981;Ozaki et al, 1982), was deferens (Garcia et al, 1981), myometrium (Grover et al, 1981;Lalanne et al, 1984), intestine (Hudgins & Bond, 1981) and airways smooth muscle (Nayler & Sparrow, 1983).…”