Dr. Long Jun Dai

Quamme GA, Dai LJ, and Rabkin SW: Dynamics of intracellular free Mg²⁺ changes in a   vascular smooth muscle cell line. American Journal of Physiology 265:H281-H288, 1993.

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Abstract Intracellular free Mg2+ concentration ( [Mg2+]i) has beeni mplicated in the pathogenesiso of hypertension. It has been postulated that Mg2+ through its antagonistic effects on intracellular Ca2+ concentration may affect tension and contractility of vascular smooth muscle cells. An established cell line of rat thoracic aorta cells (AlO) was cultured on glass cover slips, and [Mg2+], was determined by fluorescent techniques on single cells with the use of mag-fura-2. Basal [Mg2+]i was 0.52 t 0.02 mM (n = 15). Vascular smooth muscle cells were challenged with A23187 plus 5 mM MgC12 to rapidly elevate [ Mg2+ ]i. [Mg2+]i increased to a peak of 1.03 ,t 0.09 mM within l-2 s and then quickly declined to below basal levels, 0.30 & 0.03 mM, within 45-60 s despite the continued presence of A23187 and external Mg2+. The rapid removal of the Mg2+ challenget o belowb asall evelss uggeststh e presenceo of intracellular transport mechanisms,li kely in intracellular compartments or organelles. Spatial imaging studies indicated that Mg2+ is heterogeneously distributed within the cell with the greatest variations in the perinuclear region, the area of most cytosolic organelles. Vanadate, an inhibitor of P-type adenosinetriphosphatases, inhibited the removal rate from 10.2 t 0.9 to 6.8 t 1.0 FM/S. Inhibitors of intracellular Ca2+ mobilization, thapsigargin, dantrolene, and 3,4,5-trimethoxybenzoic acid 8- (diethylamino)octyl ester, inhibited Mg2+ sequestration. Ryanodine and caffeine had no effect on Mg2+ removal. Ruthenium red did not inhibit Mg2+ sequestration, but oligomycin B slowed its removal. These studies demonstrated that [Mg2+]i in vascular smooth muscle cells is carefully controlled by active mechanisms involving intracellular and plasma membrane transporters. Alteration of this control may play a role in aberrant vasoconstriction.

Dai LJ, and Quamme GA: Atrial natriuretic peptide initiates Ca²⁺ transients in isolated renal  cortical thick ascending limb cells. American Journal of Physiology 265:F592-F597, 1993.

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Abstract Atria1 natriuretic peptide initiates Ca2+ transients in isolated renal cortical thick ascending limb cells. Am. J. Physiol. 265 (Renal Fluid Electrolyte PhysioZ. 34): F592-F597, 1993.-The following studies identified and characterized atria1 natriuretic peptide (ANP) receptor-mediated Ca2+ transients in cortical thick ascending limb (CTAL) cells. Primary cell cultures were prepared from porcine kidneys by immunodissection, and intracellular Ca2+ concentration ([Ca”+]J was determined in single cells with microfluorometry. ANP (10m7M ) and its analogue,C -type natriuretic peptide (CNP, 10m7M ), elicited Ca2+t ransients [ 104 t 6 (basal levels) to 653 & 112 nM (stimulated) and from 84 t 4 to 209 & 18 nM, respectively]. Receptor-mediated [ Ca2+]i increase was dose-dependenwt ith a 50% effective concentration (EC,,) of N lo-lo M. The increment in [Ca”‘]i was due to internal release and influx across the plasma membrane. Prior treatment of ANP or CNP (10q7 M) did not markedly affect a post application of either ANP or CNP. The truncated analogue of ANP, C-ANP-(4-23), which preferentially binds to clearance receptors, elicited an increase in [Ca”+]i (82 & 1 to 427 t 41 nM). 8-Bromoguanosine 3’,5’-cyclic monophosphate (8-BrcGMP) did not alter [Ca”+]i, but pretreatment of CTAL cells with 8-BrcGMP for 30 min before agonist treatment prevented ANP-induced Ca2+ signals [83 t 5 (basal) to 88 t 5 nM (stimulated)]. These results are evidence for the existence of clearance ANP receptors in CTAL cells that may have biological functions and clearance. The functional responseso f these signal interactions may have important consequenceosn hormone actions with the CTAL.