On the putative mechanistic basis for intraoperative propofol-induced penile erections

Abstract

Propofol is an hypnotic drug used in anesthesia which was noted to induce marked vasodilation in vivo and in vitro, and to elicit intraoperative penile erections. The goal of this study was to assess the putative mechanistic basis for this later observation by con®rming its action in vivo in a rat model of penile erection, as well as by studying its effects in vitro on cultured human corporal smooth muscle cells and isolated corporal tissue strips. In vivo experiments were conducted on Fisher 344 rats anesthetized with sodium pentobarbital or propofol. Intracavernosal pressure was recorded during current stimulation of cavernous nerves. A signi®cant increase in the intracavernous pressure response was recorded at all levels neurostimulation, ranging from 1±10 mA. In vitro experiments were conducted utilizing digital imaging microscopy to assess the effects of propofol (3±12 mg/mL) on ET-1-induced (50 nM) intracellular Ca 2 transients [Ca 2 ] i in Fura-2-loaded cultured human corporal smooth muscle cells (passage 3±4) as well as to evaluate the effects of propofol on phenylephrine (PE)-induced contractile responses on isolated corporal tissue strips. With respect to the former, resting cytosolic calcium levels were not altered during preincubation with propofol alone at clinically effective concentrations (12 mg/mL). However, propofol produced a concentration-dependent decrease in the peak amplitude of the transient ET-1-induced (50 nM) [Ca 2 ] i response (P`0.001). Preincubation of the cells with calcium free/EGTA (1 mM) buffer produced a reduction in the peak amplitude of the ET-1-induced [Ca 2 ] i transient (55.5 AE 6% (n 10 cells, P`0.01)) which was indistinguishable from that produced by 8 mg/mL of propofol (53.4 AE 5.6% (n 12 cells, P`0.01)). However, propofol had no effect on the histamine-induced [Ca 2 ] i response. Lastly, preincubation of isolated human corporal tissue strips with propofol (100±200 mM; 30 min) caused a signi®cant diminution in the peak amplitude of the PE-induced contractile response. Taken together, these data indicate that the mechanistic basis for intraoperative penile erections observed with propofol may be related, at least in part, to altered transmembrane calcium¯ux through voltage-dependent calcium channels, and thus, decreased corporal smooth muscle tone.

Prostaglandin E1 activates the large-conductance KCa channel in human corporal smooth muscle cells

“…To do so we used a modi®cation of a previously described enzymatic PGE 1 activates K Ca channels in corporal smooth muscle SW Lee et al PGE 1 activates K Ca channels in corporal smooth muscle SW Lee et al dissociation protocol 19 (see Methods for details). These initial studies indicate that the myocytes so obtained have the expected morphology (Figure 1), but are apparently depolarized (resting membrane potential of 7 34 mV), relative to their explant cultured corporal smooth muscle counterparts ( 7 50 mV).…”

“…Cellular homogeneity was further veri®ed by the presence of smooth muscle speci®c aactin and myosin immunoreactivity. Cultures were maintained for no more than four passages; importantly, during this time all measured pharmacological and molecular properties observed in the intact tissue are retained in culture; for example, cAMP formation, 17,18 calcium mobilization, 14,19,20 expression or function of the gap junction protein connexin43, 16 and K channel activity. 9,10 Cell isolation protocol Corporal tissue was dissected from the human penis as described above and placed in ice-cold DMEM solution.…”

Human Vascular Smooth Muscle Cells Possess Functional CCR5

“…Cells were loaded with 10 M fura-2/AM in 0.1% dimethyl sulfoxide in HEPES-buffered solution containing145 NaCl mM, 5 KCl mM, 2.5 mM CaCl 2, 1.2 mM MgSO 4 , 11 mM glucose, and 10 mM HEPES for 1 h at 25°C. Measurements of [Ca 2ϩ ] i were performed as described previously (23,(25)(26)(27). Loaded cells were washed three times and placed in a Leiden chamber with 1 ml of HEPES-buffered solution on the stage of a Nikon Dapshot microscope (Nikon Corp., Melville, NY).…”

Mechanisms of Penile Erection and Basis for Pharmacological Treatment of Erectile Dysfunction

“…However, much of the most compelling mechanistic data concerning the role of Ca 2ϩ channels in modulating human CC smooth muscle tone have been established using digital imaging microscopy of Fura-2 loaded cultured CC smooth muscle cells. These studies have provided strong evidence for the presence and physiological relevance of transmembrane Ca 2ϩ flux through the L-type voltagedependent calcium channel in response to cellular activation with e.g., ET-1 (ET A/B receptor subtype) and phenylephrine (␣ 1 -adrenergic receptor subtype) (Christ et al, 1992b;Zhao and Christ, 1995;Staerman et al, 1997). Nifedipine-sensitive Ca 2ϩ currents have been recorded from isolated rabbit CC smooth muscle cells (Craven et al, 2004), suggesting that the individual cells may be capable of generating action potentials by the opening of L-type Ca 2ϩ channels.…”