Maturation of inositol 1,4,5-trisphosphate receptor binding in rabbit tracheal smooth muscle.
The mechanisms underlying maturational changes in agonist-mediated airway contractility remain to be identified. Since the signal transduction process coupled to airway contraction involves the Ca(2+)-mobilizing action of the second messenger, inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], the present study examined 1) whether Ins(1,4,5)P3 binding to its intracellular receptor varies with age in rabbit tracheal smooth muscle (TSM), and 2) whether Ca2+ exerts a modulatory effect on Ins(1,4,5)P3 receptor binding that is age dependent. [3H]Ins(1,4,5)P3 binding was assayed in crude TSM membrane preparations isolated from 2-week-old and adult rabbits. Monophasic Scatchard plots were obtained, reflecting a single binding site, with Hill coefficients of 0.988-0.996. The mean +/- SE values for receptor density (Bmax) and binding affinity [i.e., the dissociation constant (Kd)] were similar in the adult and immature tissues, wherein Bmax = 211 +/- 6 238 +/- 60 fmol/mg protein, respectively; and Kd = 14.1 +/- 0.2 and 11.6 +/- 1.2 nM, respectively. Addition of Ca2+ (10(-8)-10(-3) M) significantly modulated Ins(1,4,5)P3 binding, with opposing maturational effects. In adult tissues, Ca2+ produced dose-dependent inhibition of Ins(1,4,5)P3 binding to 59.5% control, whereas Ins(1,4,5)P3 binding in response to Ca2+ was significantly enhanced in the 2-week-old tissues to 183% control. Collectively, these observations demonstrate that the inherent basal binding characteristics of the Ins(1,4,5)P3 receptor are similar in maturing TSM, but that Ca2+ exerts opposite modulatory actions on Ins(1,4,5)P3 receptor binding in immature and adult tissues.(ABSTRACT TRUNCATED AT 250 WORDS)
Schramm
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Joseph Stokes, Jr., Research Institute, Department of Pediatrics, Children's Hospital of Philadelphia, Pennsylvania 19104.
Chuang
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Grunstein
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D000375:Aging / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D024510:Muscle Development; D009130:Muscle, Smooth / Q000254:growth & development / Q000378:metabolism*; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000378:metabolism*; D014132:Trachea / Q000254:growth & development / Q000378:metabolism*
D011956:Receptors, Cell Surface; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium