beta(1)-adrenergic receptors but not beta(2)-adrenergic or vasopressin receptors regulate K+ secretion in vestibular dark cells of the inner ear

Receptors were identified pharmacologically in functional studies where Ksecretion was monitored as transepithelial current (I-sc), Further, recepto rs were identified as transcripts by cloning and sequencing of reverse-tran scriptase polymerase chain reaction (RT-PCR) products. I-sc under control c onditions was 796 +/- 15 mu A/cm(2) (n = 329) in gerbilline VDC and 900 +/- 75 mu A/cm(2) (n = 6) in murine VDC. Forskolin (10(-5) M) but not 1,9-dide oxy-forskolin increased I-sc by a factor of 1.42 +/- 0.05 (n = 7). 10(-9) M Arg(8)-vasopressin and 10(-9) M desmopressin had no significant effect in gerbilline and murine VDC. Isoproterenol, norepinephrine, epi nephrine and prenalterol stimulated I-sc maximally by a factor of 1.38 +/- 0.04 (n = 7), 1.59 +/- 0.06 (n = 6), 1.64 +/- 0.03 (n = 8) and 1.37 +/- 0.03 (n = 6), re spectively. The EC50 values were (1.4 +/- 0.7) x 10(-8) M (n = 36), (2.5 +/ - 1.0) x 10(-8) M (n = 31), (1.7 +/- 0.7) x 10(-7) M (n = 36) and (5 +/- 4) x 10(-7) M (n = 32), respectively. Propanolol inhibited isoproterenol-indu ced stimulation of I-sc. Atenolol, ICI118551 and CGP20712A inhibited isopro terenol-induced stimulation of I-sc with a pK(DB) of 5.0 x 10(-8) M (pK(DB) = 7.30 +/- 0.07, n = 38), 4.4 x 10(-8) M (pK(DB) = 7.36 +/- 0.14, n = 37) and 6.8 x 10(-12) M (pK(DB) = 11.17 +/- 0.12, n = 37), respectively. RT-PCR of total RNA isolated from microdissected Vestibular labyrinth tissue usin g specific primers revealed products of the predicted sizes far beta(1)- an d beta(2)-adrenergic receptors but not for beta(3)-adrenergic receptors. Se quence analysis of the amplified cDNA fragments from gerbilline tissues rev ealed a 96.4%, 91.5% and 89.6% identity compared to rat beta(1)-, beta(2)- and beta(3)-adrenergic receptors, respectively. These results demonstrate t hat K+ secretion in VDC is under the control of beta(1)- but not beta(2)- o r beta(3)-adrenergic receptors or vasopressin-receptors.