Differences in inositol phosphate production in rat tail artery and thoracic aorta

Abstract

Pharmacomechanical coupling of vascular smooth muscle is believed to be mediated by inositol trisphosphate (IP3). Numerous studies have demonstrated an increase in inositol phosphates following tissue stimulation using either intact aortic strips or cultured cells from aorta. However, little information is available concerning inositol phosphates in vascular tissue other than in the large conduit vessel, the aorta. This present study was designed to examine the role of inositol phosphate metabolism following adrenergic stimulation of the muscular rat tail artery as compared to the aorta. Segments of thoracic aorta and tail artery from male Sprague Dawley rats were labeled with [3H]inositol and stimulated with norepinephrine. The norepinephrine concentration that resulted in a half-maximal stimulation of inositol phosphates was approximately 10(-6) M in both the aorta and tail artery. Although the sensitivity of the two vessels to norepinephrine stimulation were similar, the stimulated levels of IP, IP2, and IP3 were from 1 to 2 orders of magnitude greater in the tail artery than in aorta. IP production in aorta and tail artery was a linear function of time (from 0 to 30 min). Significant levels of IP3 (the 1,4,5-IP3 isomer as determined by HPLC) could only be detected in the tail artery and appeared to be produced optimally after 5 min of stimulation. The several order of magnitude increase in adrenergic stimulated inositol phosphate production in the tail artery was not due to either an increased magnitude of [3H]inositol incorporated into PI, PIP, and PIP2 or to a greater percentage of smooth muscle cells per unit tissue of the rat tail artery. We believe the results of this study demonstrate that the increased inositol phosphate metabolism in the vascular smooth muscle cells of the tail artery is an intrinsic property of the cell. Moreover, due to the significant levels of all inositol phosphates produced in the tail artery, this muscular artery may be a better model, as compared to the aorta, for future studies investigating pharmacomechanical coupling of vascular smooth muscle.

Effect of NG‐nitro‐L‐arginine methylester (L‐NAME) on functional and biochemical α1‐adrenoceptor‐mediated responses in rat blood vessels

“…In rat tail artery al-adrenoceptors mediate a fast and transient increase in intracellular Ca2+ which is probably the result of the mobilization of intracellular calcium and Ca2" influx through receptor-operated channels (Li et al, 1993). In addition, direct studies in tail artery rings using Fura 2 (Thorin & Atkinson, 1994) or indirect studies using inositol phosphate accumulation (Labelle & Murray, 1990;Vila et al, 1993) (Chiu et al, 1987). Therefore, it will explain why St-587, a partial agonist for contraction, did not stimulate the phosphoinositide hydrolysis in rat aorta.…”

Functional significance of muscarinic receptor expression within the proximal and distal rat vagina

“…The trichloroacetic acid solutions were extracted four times with 2 ml ethyl ether (4°C) to remove the trichloroacetate. The inositol phosphates were then separated from each other and from free inositol by the procedure of LaBelle and Murray (22). Solutions containing inositol phosphates were applied to columns of Dowex model 1X8-400 (200 -400 mesh) resin (0.5 ml) and washed with 12 ml water to remove the free inositol.…”

Deletion of SM-B, the high ATPase isoform of myosin, upregulates the PKC-mediated signal transduction pathway in murine urinary bladder smooth muscle

“…To measure 1,4,5-triphosphate (IP 3), we prelabeled murine bladders with [ 3 H] inositol, treated the tissue with LiCl (10 mM) and carbachol (0.03 mM), and rapidly froze the tissue in liquid N 2. The tissue was then extracted with trichloroacetic acid and the inositol phosphates were separated by Dowex chromatography (28). The radioactivity was measured in a Packard 1500 Tri-Carb liquid scintillation counter and the results were normalized as disintegrations per minute (DPMs) per 15 mg bladder tissue.…”