Beta1-adrenergic receptors but not beta2-adrenergic or vasopressin receptors regulate K+ secretion in vestibular dark cells of the inner ear.
Receptors were identified pharmacologically in functional studies where K+ secretion was monitored as transepithelial current (Isc). Further, receptors were identified as transcripts by cloning and sequencing of reverse-transcriptase polymerase chain reaction (RT-PCR) products. Isc under control conditions was 796 +/- 15 microA/cm2 (n = 329) in gerbilline VDC and 900 +/- 75 microA/cm2 (n = 6) in murine VDC. Forskolin (10(-5) m) but not 1, 9-dideoxy-forskolin increased Isc by a factor of 1.42 +/- 0.05 (n = 7). 10(-9) m Arg8-vasopressin and 10(-9) m desmopressin had no significant effect in gerbilline and murine VDC. Isoproterenol, norepinephrine, epinephrine and prenalterol stimulated Isc 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), respectively. 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-induced stimulation of Isc. Atenolol, ICI118551 and CGP20712A inhibited isoproterenol-induced stimulation of Isc with a pKDB of 5.0 x 10(-8) m (pKDB = 7.30 +/- 0.07, n = 38), 4.4 x 10(-8) m (pKDB = 7.36 +/- 0.14, n = 37) and 6.8 x 10(-12) m (pKDB = 11.17 +/- 0.12, n = 37), respectively. RT-PCR of total RNA isolated from microdissected vestibular labyrinth tissue using specific primers revealed products of the predicted sizes for beta1- and beta2-adrenergic receptors but not for beta3-adrenergic receptors. Sequence analysis of the amplified cDNA fragments from gerbilline tissues revealed a 96.4%, 91.5% and 89.6% identity compared to rat beta1-, beta2- and beta3-adrenergic receptors, respectively. These results demonstrate that K+ secretion in VDC is under the control of beta1- but not beta2- or beta3-adrenergic receptors or vasopressin-receptors.
Cell Physiology Laboratory, Anatomy & Physiology Department, Kansas State University, Manhattan, KS 66506, USA.
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Wangemann
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Liu
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Shimozono
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Scofield
D058665:Adrenergic beta-1 Receptor Agonists; D058671:Adrenergic beta-1 Receptor Antagonists; D058666:Adrenergic beta-2 Receptor Agonists; D058672:Adrenergic beta-2 Receptor Antagonists; D000818:Animals; D002999:Clone Cells; D005576:Colforsin / Q000494:pharmacology; D017931:DNA Primers; D007758:Ear, Inner / Q000166:cytology*; D004553:Electric Conductivity; D004837:Epinephrine / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism; D005849:Gerbillinae; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D009638:Norepinephrine / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D011188:Potassium / Q000378:metabolism*; D011433:Propranolol / Q000494:pharmacology; D012333:RNA, Messenger / Q000737:chemistry; D051381:Rats; D018342:Receptors, Adrenergic, beta-1 / Q000235:genetics / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics / Q000378:metabolism*; D017483:Receptors, Vasopressin / Q000378:metabolism*; D014158:Transcription, Genetic; D014667:Vasopressins / Q000494:pharmacology; D014722:Vestibule, Labyrinth / Q000166:cytology*
D058665:Adrenergic beta-1 Receptor Agonists; D058671:Adrenergic beta-1 Receptor Antagonists; D058666:Adrenergic beta-2 Receptor Agonists; D058672:Adrenergic beta-2 Receptor Antagonists; D017931:DNA Primers; D012333:RNA, Messenger; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D017483:Receptors, Vasopressin; D014667:Vasopressins; D005576:Colforsin; D011433:Propranolol; D007545:Isoproterenol; D011188:Potassium; D009638:Norepinephrine; D004837:Epinephrine