Intracorporal injection ofhSlocDNA restores erectile capacity in STZ-diabetic F-344 rats in vivo

Abstract

The ability of gene transfer with the pore-forming subunit of the human maxi-K channel ( hSlo) to ameliorate the decline in erectile capacity commensurate with 12–24 wk of streptozotocin (STZ)-diabetes was examined in 181 Fischer-344 rats. A 2-mo period of STZ-diabetes was induced before gene transfer, and erectile capacity was evaluated by measuring the intracavernous pressure response (ICP) to cavernous nerve (CN) stimulation (ranging from 0.5 to 10 mA). In the first series of experiments, ANOVA revealed increased CN-stimulated ICP responses at 1 and 2 mo postinjection of 100 μg pcDNA- hSlo compared with control values. A second series of experiments further examined the dose dependence and duration of gene transfer. The ICP response to submaximal (0.5 mA) and maximal (10 mA) nerve stimulation was evaluated 3 or 4 mo postinjection of a single dose of pcDNA- hSlo ranging from 10 to 1,000 μg. ANOVA again revealed that hSlo overexpression was associated with increased CN-stimulated ICP responses compared with responses in corresponding control animals. Histological studies revealed no immune response to the presence of hSlo. PCR analysis documented that expression of both plasmid and transcript were largely confined to the corporal tissue. In the third series of pharmacological experiments, hSlo gene transfer in vivo was associated with iberiotoxin-sensitive relaxation responses to sodium nitroprusside in corporal tissue strips in vitro. The latter data indicate that gene transfer produces functional maxi-K channels that participate in the modulation of corporal smooth muscle cell tone. Taken together, these observations suggest a fundamental diabetes-related change in corporal myocyte maxi-K channel regulation, expression, or function that may be corrected by expression of recombinant hSlo.

Hypercontractility and impaired sildenafil relaxations in the BKCachannel deletion model of erectile dysfunction

“…Previous investigations established that the BK Ca channel has a central role in the modulation of nonvascular (26,37) and vascular contractility (18,28), as well as in the corpus cavernosum (11,12,25). The suggested mechanism of BK Ca channel function is linked to the hyperpolarization of smooth muscle cells and a concomitant decrease in transmembrane Ca 2ϩ flux through L-type VDCC (7,18).…”

“…Blocking the BK Ca channel with tetraethylammonium ions or charybdotoxin led to an increase of phenylephrine (PE)-induced contractions of CCSM strips in vitro (34). In aged or diabetic rats, intracavernous injection of cDNA encoding the human BK Ca channel led to a reversal of ED (11,25). Consistent with the significant role of BK Ca channels to oppose smooth muscle contractility, precontracted CCSM strips from mice lacking the BK Ca channel (Kcnma1 Ϫ/Ϫ , also called Slo Ϫ/Ϫ ) exhibited pronounced force fluctuations in the presence of the ␣-adrenergic receptor agonist PE and reduced relaxations in response to nerve stimulations compared with wild-type mice (Slo ϩ/ϩ ) (42).…”

“…The BK Ca channel is an attractive target in the treatment of vascular and lower urinary tract disorders, including urinary incontinence and ED. Kcnma1 (Slo) gene therapy has been shown to ameliorate ED in rodents (11), and recently in humans (22).…”

Gene transfer with a vector expressing Maxi-K from a smooth muscle-specific promoter restores erectile function in the aging rat

“…Thus, with respect to ED, despite the more limited smooth muscle expression profile, the CN-stimulated ICP response for pSMAA-hSlo compares quite favorably to that observed with hSlo expression driven by the heterologously expressed CMV promoter (the vector used in the recently completed Phase I human clinical trial), [17][18][19][20] as well as our prior preclinical observations with pcDNA/hSlo. [14][15][16] Again, it is important to keep in mind that gene transfer with both promoters produces an ICP/BP ratio commensurate with an erection; that is, an ICP/BP ratio of more than 0.6. As discussed elsewhere, the probability of visualizing an erection during CN stimulation increases dramatically as the ICP/BP ratio becomes 0.6 or more.…”

“…[14][15][16] These studies were performed with a naked DNA vector, pcDNA-hSlo, in which Slo gene expression is driven by the cytomegalovirus (CMV) promoter, which functions in the majority of both human and animal tissues. A bacterial selectable marker (the penicillin-resistance gene, ampR) is present in this plasmid.…”