Effects of forskolin and cyclic nucleotides on isometric force in rat aorta

Abstract

The present study was undertaken to determine the extent to which cyclic nucleotide-induced relaxation in the intact rat aorta is mediated at the level of the contractile system. The relaxant effects of the cyclic nucleotide analogues [8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) and dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP)] and forskolin were examined in both the intact vessel and a Triton X-100-skinned preparation of rat thoracic aorta. Relaxation of a norepinephrine-induced contraction was essentially complete 30 min after the addition of 50 microM 8-BrcGMP [% relaxation = 87.2 +/- 4.4% (n = 4)], 100 microM DBcAMP [98.2 +/- 1.2% (n = 4)], and 1 microM forskolin [107.0 +/- 3.3% (n = 5)]. These same doses were ineffective in relaxing precontracted skinned rat aortic rings compared with the relaxation achieved in the intact vessel. The largest relaxation in the skinned aortas was achieved with the addition of 1 microM forskolin [17.4 +/- 1.5% (n = 4)]. The addition of catalytic subunit of cAMP-dependent protein kinase had no effect on isometric tension in the precontracted skinned aorta. Preincubation with the cyclic nucleotide analogues or forskolin in a low-Ca2+ solution (pCa less than 8) was also ineffective in inhibiting subsequent isometric tension development. Our results suggest that only a very small fraction of the relaxation with cyclic nucleotides and forskolin in the intact rat aorta is due to the action of these agents at the level of the contractile system.

Ca(2+)‐independent change in phosphorylation of the myosin light chain during relaxation of ferret aorta by vasodilators.

“…The affinity of MLCK for the Ca2+-calmodulin complex has been reported to decrease when it is phosphorylated by cyclic AMP-dependent protein kinase, resulting in inhibition of MLCK activity (Conti & Adelstein, 1981). Others have reported that cyclic AMP-dependent protein kinase has little direct effect on MLCK activity in vascular smooth muscle (Gerthoffer, Trevethick & Murphy, 1984;McMahon & Paul, 1986). The relationship between [Ca2+]i and MLC phosphorylation does not change with increasing compared to decreasing [Ca2+]i, i.e.…”

Contractile Force Is Enhanced in Aortas from Pendrin Null Mice Due to Stimulation of Angiotensin II-Dependent Signaling

“…where 1.06 g/cm 3 was used as an estimate of tissue density [20]. This approach yields values for vessel thickness that are similar to thickness measurements determined by morphometry [21].…”

“…At the end of the experiment, rings were cut open longitudinally and the muscle dimensions (segment length and circumference) were measured with a calibrated optical micrometer [20]. The tissue was then gently blotted and weighed (wet weight).…”

Evidence for decrease in myofilament responsiveness to Ca2+ during hypoxia in spontaneously active vascular smooth muscle in rats

“…In intact SM, this would cause a rise in intracellular cAMP; but the problem of how low Po2 may stimulate cAMP production in skinned SM remains. It was established 400 Ca" RESPONSIVENESS OF MYOFILAMENTS IN HYPOXIA 401 (McMahon & Paul, 1986) that adenylate cyclase, which is located predominantly on plasma membrane, retains its activity in skinned SM, because the adenylate cyclase stimulant forskolin induces noticeable (17-4+1 5 %) relaxation in skinned SM. Additionally, it is known that a guanine nucleotide-binding protein (G protein) has been implicated in the transduction of signal from several types of receptors and regulates adenylate cyclase activity.…”