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B A Weaver

Publications and source records attributed to B A Weaver.

8 recordsLinked to original sources
PubMed1995

Myosin light chain kinase phosphorylation in swine carotid artery contraction and relaxation.

We investigated the role of myosin light chain kinase (MLCK) phosphorylation in regulating the sensitivity of vascular smooth muscle myosin light chain (MLC) phosphorylation to intracellular Ca2+ concentration ([Ca2+]i). 32PO4-loaded swine carotid arteries were stimulated with histamine or high K+, MLCK was isolated, and the relative phosphorylation of tryptic peptides was measured. In nonlabeled tissues, we measured [Ca2+]i with aequorin, MLCK activity ratio, MLC phosphorylation, and force. A comparison of MLCK phosphorylation on peptide A (mol P in site A/mol MLCK) and MLCK activity ratio showed an inverse relation, suggesting that MLCK site A phosphorylation can regulate the Ca2+ sensitivity of MLCK. MLCK site A phosphorylation and MLCK activity ratio depended on [Ca2+]i. Histamine stimulation yielded greater MLC phosphorylation than high K+ stimulation over a range of [Ca2+]i; however, there were no apparent stimulus-dependent differences in MLCK phosphorylation, suggesting that stimulus-dependent differences in the Ca2+ sensitivity of MLC phosphorylation are not based on differences in MLCK phosphorylation. We also determined whether MLCK phosphorylation was involved in adenosine 3',5'-cyclic monophosphate-mediated relaxation. In histamine-contracted tissues, forskolin decreased [Ca2+]i, MLC phosphorylation, and force. MLCK phosphorylation decreased to an extent consistent with the decrease in [Ca2+]i. In KCl-stimulated tissues, forskolin did not alter [Ca2+]i or increase MLCK phosphorylation but forskolin did decrease MLC phosphorylation. Thus, in swine carotid artery, MLCK phosphorylation appears to be regulated exclusively by Ca2+ and plays little role in stimulus-dependent differences in Ca2+ sensitivity of MLC phosphorylation or in mediating forskolin-induced relaxation.

Animals↗
PubMed1991

Adenosine triphosphate induces a low [Ca2+]i sensitivity of phosphorylation and an unusual form of receptor desensitization in smooth muscle.

The contractile sensitivity of smooth muscle to changes in myoplasmic [Ca2+] is dependent on the form of stimulation. Both myosin phosphorylation and force are less sensitive to increases in [Ca2+]i derived from Ca2+ entry through L-type Ca2+ channels than to increases in [Ca2+] induced by agents which release internal Ca2+ stores. We hypothesized that activation of receptor-operated channels should produce a [Ca2+]i sensitivity similar to that induced by opening L channels. Aequorin-estimated myoplasmic [Ca2+] and myosin light chain phosphorylation were measured in swine carotid media tissues stimulated with ATP, an activator of the only known receptor-operated cation channel in smooth muscle. ATP, via activation of a P2x purinergic receptor, induced large, transient increases in [Ca2+]i, yet only small transient elevations in phosphorylation or force. Rapid desensitization to ATP was partially, but not completely, caused by hydrolysis of ATP into adenosine since 1) alpha-beta-methylene ATP (a poorly hydrolyzable analog of ATP) produced larger, yet still transient increases in [Ca2+]i, phosphorylation, and force; 2) BW A1433U, a P1 (adenosine) receptor antagonist, enhanced ATP-induced contractions; and 3) ATP, but not alpha-beta-methylene ATP increased bath [adenosine]. The [Ca2+]i sensitivity of phosphorylation during P2x receptor activation was similar to that observed with KCl-depolarization-induced opening of L channels, supporting the hypothesis that transplasmalemmal Ca2+ influx produces less phosphorylation and force than mobilization of intracellular Ca2+ stores. Cumulative additions of higher alpha-beta-methylene ATP concentrations induced repeated transient contractions, indicative of an unusual form of receptor desensitization which could be explained if the affinity of the P2x receptor for ATP, but not the receptor number were rapidly reduced.

Adenosine Triphosphate↗
PubMed1991

Depolarization decreases the [Ca2+]i sensitivity of myosin light-chain kinase in arterial smooth muscle: comparison of aequorin and fura 2 [Ca2+]i estimates.

Histamine stimulation of swine arterial smooth muscle is associated with a high [Ca2+]i sensitivity for increases in myosin light-chain phosphorylation. In contrast, KCl depolarization produces a relatively lower [Ca2+]i sensitivity (i.e., similar increases in [Ca2+]i induce less myosin phosphorylation). We evaluated whether 1) artifacts in the methodology for measuring [Ca2+]i or 2) true alterations in the [Ca2+]i sensitivity of myosin light-chain kinase were responsible for these apparent changes in the [Ca2+]i sensitivity of phosphorylation. The [Ca2+]i sensitivity of phosphorylation was higher with histamine stimulation regardless of whether the [Ca2+]i indicator was aequorin (which was loaded intracellularly by reversible hyperpermeabilization) or Fura 2 (which was loaded intracellularly by incubation of the tissues in Fura 2 AM). Aequorin and Fura 2 appeared to detect qualitatively similar stimulus-induced changes in [Ca2+]i with the exception that the initial response to histamine stimulation was different (histamine initially induced a large aequorin light transient and a relatively smaller increase in Fura 2 fluorescence). The [Ca2+]i sensitivity of myosin light-chain kinase extracted from KCl depolarized tissues was lower than the [Ca2+]i sensitivity of myosin light-chain kinase extracted from unstimulated or histamine stimulated tissues. These results suggest that depolarization specifically modifies myosin light-chain kinase to decrease its [Ca2+]i sensitivity. Changes in the [Ca2+]i sensitivity of myosin light-chain phosphorylation are not an artifact of the [Ca2+]i measurement technique.

Aequorin↗
PubMed1990

[Ca2+], not diacylglycerol, is the primary regulator of sustained swine arterial smooth muscle contraction.

Sustained smooth muscle contraction has been proposed to be regulated by either 1) sustained increases in intracellular Ca2+ concentration [(Ca2+]i)-dependent myosin phosphorylation or 2) diacylglycerol-dependent protein kinase C activation. We measured diacylglycerol mass with the diacylglycerol kinase assay and myoplasmic [Ca2+] with aequorin in swine carotid medial smooth muscle. Sustained and significant increases in [Ca2+], myosin light chain phosphorylation, and isometric stress were observed with histamine or endothelin stimulation. Neither stimuli, however, induced significant increases in diacylglycerol mass. Relaxation of histamine-stimulated tissues was induced by removal of histamine or removal of extracellular CaCl2 in the continued presence of histamine. The rate of decline of both [Ca2+] and force was similar in both protocols, suggesting that removal of Ca2+ (without removing the stimulus) was equivalent to removal of the stimulus. These data suggest that [Ca2+]i is the primary regulator of sustained swine arterial smooth muscle contraction, whereas diacylglycerol has, at most, only a minor role.

Alkaloids↗
PubMed1985

Enalapril maleate versus captopril. A comparison of the hormonal and antihypertensive effects.

24 hypertensive patients were randomised into 2 groups to compare the antihypertensive effects of enalapril and captopril over a 10-week period. In the hydrochlorothiazide run-in period, blood pressure was reduced from 171 +/- 4/109 +/- 1mm Hg to 160 +/- 4/103 +/- 1mm Hg (p less than 0.05). Angiotensin-converting enzyme (ACE) inhibition decreased blood pressure to 132 +/- 3/87 +/- 2mm Hg. Captopril decreased diastolic blood pressure significantly more after 3 hours than enalapril (-24 versus -17mm Hg, p less than 0.05). After 10 weeks of therapy, this antihypertensive response was maintained at 134 +/- 3/83 +/- 1mm Hg. There was no difference between the captopril and enalapril treated groups. Acute and chronic responses of plasma renin activity, plasma aldosterone and ACE were determined. There was an acute positive correlation between the rise in plasma renin activity and the fall in blood pressures with captopril but not with enalapril. With chronic treatment there was no difference in the ability of either of the 2 drugs to reduce blood pressure, inhibit ACE, reduce aldosterone or stimulate plasma renin activity.

Adult↗
PubMed1985

Captopril versus enalapril maleate: a comparison of antihypertensive and hormonal effects.

The antihypertensive effects of captopril and enalapril maleate were studied over a 10-week period in 24 hypertensive patients randomized into captopril or enalapril treatment groups. Prestudy blood pressure was 171 +/- 4/109 +/- 1 mm Hg and after 4 weeks of hydrochlorothiazide 160 +/- 4/103 +/- 1 (p less than 0.05). With the addition of converting enzyme inhibitor to hydrochlorothiazide the blood pressure decreased at 3 h to 132 +/- 3/87 +/- 2 in the subjects. The diastolic blood pressure decreased acutely more with captopril (-24) than with enalapril (-17) (p less than 0.05). After 10 weeks of combined therapy the depressor response was maintained (134 +/- 3/83 +/- 1) and there was no difference between the diastolic blood pressure in the two groups treated with captopril and enalapril. Acute and chronic responses of plasma renin activity, plasma aldosterone, and converting enzyme to the angiotensin-converting enzyme inhibitor were determined. There was a significant correlation between the acute fall in diastolic blood pressure and rise in plasma renin activity in patients treated with captopril but not with enalapril. In conclusion, there is an acute depressor response with converting enzyme inhibition which is more pronounced with captopril than with enalapril and which correlates with an increase in plasma renin activity. With more prolonged treatment, the two drugs show equivalent efficacy in reducing blood pressure, inhibiting angiotensin-converting enzyme, reducing aldosterone, and stimulating plasma renin activity.

Adult↗
PubMedDate not supplied

Tyrosine phosphorylation and regulation of swine carotid artery contraction.

Regulation of [Ca2+]i and modulation of the [Ca2+]i sensitivity of myosin phosphorylation in smooth muscles may involve phosphorylation of one or more proteins on tyrosine residues. We tested this hypothesis by measuring tyrosine phosphorylation of proteins extracted from swine carotid artery and separated by SDS gel electrophoresis. Tyrosine phosphorylation was estimated by the binding of antiphosphotyrosine antibodies to proteins in SDS gels. We found four bands with approximate molecular weights of 120, 110, 85 and 75 kD in which tyrosine phosphorylation increased 1 min after histamine stimulation. After washout of histamine, dephosphorylation of the proteins in these four bands occurred at a slower rate than relaxation. Tyrosine phosphorylation of these four protein bands did not correlate with the [Ca2+]i sensitivity of myosin phosphorylation following agonist or high [K+]o stimulation. Phorbol dibutyrate stimulation also induced tyrosine phosphorylation of these four protein bands. These data suggest that tyrosine phosphorylation of the proteins in these four bands may be involved in the initial phase of swine carotid artery contraction. However, there was, at most, only a minor involvement of tyrosine phosphorylation of these four protein bands in the sustained phase of contraction or in the regulation of [Ca2+]i sensitivity of myosin phosphorylation in the swine carotid artery. These data do not rule out a role for other, less abundant tyrosine phosphoproteins in the regulation of sustained contraction or the [Ca2+]i sensitivity of myosin phosphorylation.

Animals↗