Specific binding of [3H]inositol 1,4,5-trisphosphate to bovine iris sphincter microsomal membranes.
The binding of [3H]inositol 1,4,5-trisphosphate [( 3H]IP3) to bovine iris sphincter microsomes has been shown to be rapid, reversible and saturable. The microsomal preparation contained a single population of high affinity sites for [3H]IP3 (Kd = 3.52 nM, Bmax = 218 fmol/mg protein). The concentration of IP3 receptors in the iris sphincter is much higher than that of the corneal epithelium (99 fmol/mg protein), but considerably lower than that of the rat brain cortex (2250 fmol/mg protein). Kinetic studies on bovine iris sphincter microsomes showed: (a) an extremely rapid time-course of [3H]IP3 binding with a half-maximal binding achieved in 55 sec and reached equilibrium by 10 min; (b) that the [3H]IP3 binding was readily reversible with a t1/2 value of 36 sec, and (c) that the specificity of IP3 receptor sites can be demonstrated by their lack of affinity for 1,3,4-IP3, IP6 and cyclic IP1, and a much weaker affinity for IP1, IP2 and IP4. The results presented provide the first data on the affinity of [3H]IP3 to smooth muscle microsomal membranes. These data support the hypothesis that the [3H]IP3 binding reported here represents a putative physiologically important IP3 receptor which can be quantified in iris sphincter membranes.
Akhtar
R A
RA
Department of Cell and Molecular Biology, Medical College of Georgia, Augusta 30912-2100.
Abdel-Latif
A A
AA
D000818:Animals; D001667:Binding, Competitive; D015220:Calcium Channels; D002417:Cattle; D002540:Cerebral Cortex / Q000378:metabolism; D003315:Cornea / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007425:Intracellular Membranes / Q000378:metabolism; D007498:Iris / Q000378:metabolism*; D007700:Kinetics; D008861:Microsomes / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D015544:Inositol 1,4,5-Trisphosphate