Modulation of Adrenergic Responses of Human Vas Deferens by K+ Channel Inhibitors

Abstract

OBJECTIVESThe present study was designed to evaluate the role of K ϩ channels in the adrenergic responses of human vas deferens as well as the intervention of dihydropyridine-sensitive Ca 2ϩ channels on modulation of adrenergic responses by K ϩ channel inhibitors. METHODSRing segments of the epididymal part of the vas deferens were taken from 32 elective vasectomies and mounted in organ baths for isometric recording of tension. We then studied the effects of K ϩ channel blockers on neurogenic and norepinephrine-induced contractile responses. RESULTSAddition of tetraethylammonium (TEA, 10 Ϫ3 M), a nonspecific K ϩ channel blocker, or charybdotoxin (10 Ϫ7 M), a nonselective inhibitor of large-and intermediate-conductance Ca 2ϩ -activated K ϩ channel, increased the contractile responses to norepinephrine and electrical field stimulation-induced contractions (P Ͻ .01), whereas iberiotoxin (10 Ϫ7 M), a selective blocker of large-conductance Ca 2ϩ -activated K ϩ channels, apamin (10 Ϫ6 M), a blocker of small-conductance Ca 2ϩ -activated K ϩ channels, or glibenclamide (10 Ϫ5 M), an inhibitor of ATP-sensitive K ϩ channels, were without effect. TEA-and charybdotoxin-induced potentiation of contractions elicited by electrical field stimulation and norepinephrine was blocked by L-type Ca 2ϩ channel blocker nifedipine (10 Ϫ6 M). CONCLUSIONSThe results suggest that charybdotoxin-sensitive, but iberiotoxin-insensitive, K ϩ channels are activated by stimulation with norepinephrine and electrical field stimulation to counteract the adrenergic-induced contractions of human vas deferens. Thus, inhibition of these channels increases significantly the contraction, an effect that appears to be mediated by an increase in Ca 2ϩ entry through L-type voltage-dependent Ca 2ϩ channels. UROLOGY 76: 1518.e7-1518.e12, 2010.

Role of Ca2+-activated K+ channels and Na+,K+-ATPase in prostaglandin E1- and E2-induced inhibition of the adrenergic response in human vas deferens

“…Several agents could inhibit neurotransmitter release from nerve endings in vas deferens through a mechanism that involves activation of K + channels. In human vas deferens, charybdotoxin-sensitive, iberiotoxin-insensitive, K + channels modulate the adrenergic contrac- Prostaglandin E 2 (-log M) tile response by interfering with Ca 2+ entry through dihydropyridine Ca 2+ channels [9]. Furthermore, it has been shown that K + channels are involved in the prejunctional inhibitory effects of atrial natriuretic factor in the rabbit isolated vas deferens [12] and in the a 2 -adrenoceptor-mediated inhibition in rat vas deferens [13].…”

“…K + channels modulate the adrenergic contractile responses in human vas deferens [9] and several agents have been shown to inhibit neurotransmitter release from nerve endings through a mechanism that involves the opening of prejunctional K + channels, membrane hyperpolarization and reduction in Ca 2+ influx via voltage-activated Ca 2+ channels [10,11]. In vas deferens, it has been demonstrated that K + channels are involved in the prejunctional inhibitory effects of atrial natriuretic factor [12], a 2 -adrenoceptor agonists [13] and sildenafil, an inhibitor of phosphodiesterase 5 [14].…”

Role of Calcium-Activated Potassium Channels in the Genesis of 3,4-Diaminopyridine-Induced Periodic Contractions in Isolated Canine Coronary Artery Smooth Muscles

“…The drugs that were used in the present study were: 1) inhibitors of calcium-activated-potassium channels (K Ca ); largeconductance K Ca inhibitors, iberiotoxin (IbTX; Sigma-Aldrich Japan, Tokyo, Japan) (Latorre et al, 1989;Marchenko and Sage, 1996); charybdotoxin (ChTX; Sigma-Aldrich Japan) (Miller et al, 1985); small-conductance K Ca inhibitor, apamine (Muraki et al, 1997); 2) CaCl 2 (Wako Pure Chemicals, Osaka, Japan); 3) inhibitors of L-type voltage-gated-calcium channels (Ca V ), nifedipine (Wako Pure Chemicals) (Medina et al, 2010), verapamil (Wako Pure Chemicals) (Ko et al, 2010); 4) agonist of L-type Ca V , Bay K8644 [S-(Ϫ)-1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-[trifluoromethyl]phenyl)-3-pyridine carboxylic acid methyl ester] (Sigma-Aldrich Japan) (Amobi et al, 2010); 5) acidic and alkaline substances, HCl, lactic acid, NaOH, NaHCO 3 (Wako Pure Chemicals); 6) inhibitors of ion pumps: Na-pump (K ϩ -Na ϩ -ATPase) inhibitor, ouabain (Sigma-Aldrich Japan) (Briggs et al, 1996); 7) hybrid of ATP-sensitive potassium channel (K ATP ) opener and nitrate: nicorandil (Chugai Pharmaceutical Co, Tokyo, Japan) (Uchida et al, 1978;Yanagisawa et al, 1979); 8) K ATP opener, pinacidil (Wako Pure Chemicals) (Davies et al, 2010); 9) K ATP inhibitor, glibencramide (Wako Pure Chemicals) (Lindauer et al, 2003;Medina et al, 2010); 10) drugs that affect the sarcoplasmic reticulum (SR), caffeine (Wako Pure Chemicals) (Somlyo and Somlyo, 1976), dantrolene (Wako Pure Chemicals) (Kuba, 1980); 11) drugs that affect the mitochondria, oligomycin (Sigma-Aldrich Japan) (Visneskii et al, 1980); 12) ␤-adrenergic receptor agonist, isoproterenol (Sigma-Aldrich Japan) (Petkov and Nelson, 2005) Data Presentation. Because PCs of coronary artery rings obtained from the same beagle tend to provide a uniform response to a given stimulus (Uchida, 1985), each study group was composed of rings obtained from different beagles; therefore, the number of rings also indicated the number of beagles in the present study.…”

“…The cycle length of these waves ranged from 5 s to 5 min, and the waves were not accompanied by a spikeand-plateau depolarization and contraction ( Fig. 2C), nor were they inhibited by nifedipine, which inhibits Ca V (Medina et al, 2010).…”

P2X1 Receptors Localized in Lipid Rafts Mediate ATP Motor Responses in the Human Vas Deferens Longitudinal Muscles1

“…The functional role of ATP as a cotransmitter in human vas deferens transmission remains unclear. Reports based on studies performed mainly with the circular layer of the tissue discarded the role of ATP because the contractions in response to nerve stimulation were antagonized by a 1 -adrenoceptor antagonists, suggesting the lack of a purinergic component in human vas deferens cotransmission [7][8][9][10]. Moreover, Banks et al [11] showed evidence favoring the involvement of P2X1 receptors (P2X1R) and a 1 -adrenoceptors in the motor contractions of the human vas deferens, although no dissection of the tissue muscle layers was performed.…”