Characterization of muscarinic acetylcholine receptor in rat Sertoli cells

This study was designed to characterize muscarinic acetylcholine receptors (mAChRs) in primary cultured Sertoli cells from 30-d-old rats. RT-PCR was performed, and five PCR products corresponding to m1-m5 mAChR mRNA subtypes were detected in these cells. Ribonuclease protection assay further confirmed the presence of protected products for m1, m2, m3, and m4 mAChR transcripts. Radioligand binding studies and the analysis of changes in intracellular signaling pathways after cell exposure to carbachol were performed to study mAChRs at the protein level. Scatchard analysis revealed one single class of [(3)H]quinuclidinyl benzilate binding sites. Carbachol produced a reduction on forskolin-induced intracellular cAMP accumulation in Sertoli cells. This effect was reversed by atropine, methoctramine, and tropicamide but not by p-fluoro-hexahydro-sila-difenidol or pirenzepine. Carbachol also induced an increase on total [(3)H]-inositol phosphates content, an effect antagonized by atropine, p-fluoro-hexahydro-sila-difenidol, or pirenzepine but not by methoctramine. Thus, mAChR activation in Sertoli cell is linked to both adenylyl cyclase inhibition and to phosphoinositide hydrolysis. Furthermore, gel shift assays indicated that carbachol also induced a time-dependent stimulation of the activator protein-1 DNA-binding activity, suggesting that activation of mAChRs may play a role in the modulation of gene expression in Sertoli cells. Taken together, these results indicate that mAChRs are present at mRNA and protein level in rat Sertoli cells.

Characterization of muscarinic acetylcholine receptors in the rat epididymis

The aim of the present study was to characterize the muscarinic acetylcholine receptor subtypes present in the caput and cauda of rat epididymis. The specific binding of [3H]quinuclidinyl benzilate ([3H]QNB) to epididymal membranes was time dependent, temperature dependent, and saturable. The cauda epididymis showed higher affinity to [3H]QNB and higher muscarinic receptor density when compared to the caput region. The [3H]QNB binding was tested in competition studies with different muscarinic receptor antagonists. Each antagonist tested displaced [3H]QNB bound to caput and cauda epididymal membrane with similar affinity. Correlation among the negative logarithm of inhibition constant values (pK(i)) for these antagonists obtained in the epididymis with their correspondent published pK(i) values obtained in tissues that expressed each receptor subtype (M1, M2, M3, and M4) indicated that the muscarinic receptors present in caput and cauda epididymis belong to the muscarinic M2 receptor subtype. When reverse transcription-polymerase chain reaction was used to identify muscarinic receptor mRNA subtypes in the epididymis, only m2 transcripts were detected in the caput region, while both m2 and m3 mRNA subtypes were observed in the cauda region. In conclusion, these results demonstrate that muscarinic receptors are present in the rat epididymis, with expression levels dependent on the region of the epididymis analyzed. Thus, the cholinergic neurotransmitter in the epididymis may be a factor controlling contractility and/or the luminal fluid microenvironment.

Expression and pharmacological characterization of alpha1-adrenoceptors in rat seminal vesicle

In the present study, we investigated the alpha1-adrenoceptor subtypes mediating adrenaline-induced contractions of the rat seminal vesicle by using functional studies. The reverse transcription combined with polymerase chain reaction (RT-PCR) was also used to identify of alpha1-adrenoceptor mRNA subtypes. The rank order of potency of alpha1-adrenoceptor antagonists in blocking the contractile effects of adrenaline was: prazosin = WB 4101 >>> BMY 7378 > chloroethylclonidine, indicating the presence of alpha1A-adrenoceptors in the rat seminal vesicle. In the presence of nifedipine, there was a 76% reduction in the adrenaline-induced contractions. The nifedipine-insensitive component (24%) of the contractile response to adrenaline was unaffected by chloroethylclonidine. A small pool of spare alpha1-adrenoceptors for adrenaline (0.10%) was also detected. All three alpha1-adrenoceptor subtypes were amplified when RT-PCR was performed on total RNA isolated from rat seminal vesicle. In conclusion, these data indicate the presence of three alpha1-adrenoceptor mRNA subtypes, but only alpha1A-adrenoceptors are involved in the rat seminal vesicle contraction.

Androgen-dependent protein interactions within an intron 1 regulatory region of the 20-kDa protein gene

The 20-kDa protein gene is androgen regulated in rat ventral prostate. Intron 1 contains a 130-base pair complex response element (D2) that binds androgen (AR) and glucocorticoid receptor (GR) but transactivates only with AR in transient cotransfection assays in CV1 cells using the reporter vector D2-tkCAT. To better understand the function of this androgen-responsive unit, nuclear protein interactions with D2 were analyzed by DNase I footprinting in ventral prostate nuclei of intact or castrated rats and in vitro with ventral prostate nuclear protein extracts from intact, castrated, and testosterone-treated castrated rats. Multiple androgen-dependent protected regions and hypersensitive sites were identified in the D2 region with both methods. Mobility shift assays with 32P-labeled oligonucleotides spanning D2 revealed specific interactions with ventral prostate nuclear proteins. Four of the D2-protein complexes decreased in intensity within 24 h of castration. UV cross-linking of the androgen-dependent DNA binding proteins identified protein complexes of approximately 140 and 55 kDa. The results demonstrate androgen-dependent nuclear protein-DNA interactions within the complex androgen response element D2.

Are imidazoline receptors involved in sympathetic neurotransmission in rat vas deferens?

1. An involvement of imidazoline receptors in the modulation of neurotransmitter release was investigated in the prostatic portion of the rat vas deferens stimulated transmurally at 0.2 Hz or by single pulses. 2. Idaxozan and yohimbine induced a concentration-dependent potentiation of the contractile response to 0.2-Hz transmural stimulation in the epididymal and prostatic portion of the vas. 3. After reserpine treatment, idazoxan, but not yohimbine, still potentiated the contractile response, suggesting a possible involvement of imidazoline receptors. 4. Clonidine and rilmenidine, agonists with different affinities to alpha 2-adrenoceptors and imidazoline receptors, inhibited with the same potency the contractile responses to a single pulse transmural stimulation. 5. Yohimbine (a selective alpha 2-adrenoceptor antagonist) antagonized the inhibitory concentration effect curve to rilmenidine in a competitive manner. pA2 values for idaxozan (an antagonist to alpha 2-adrenoceptors and imidazoline receptors) were not different when noradrenaline or rilmenidine were used as agonists. Phenoxybenzamine blocked the effect of both agonists. 6. Thus, the potency relationship of agonists, as well as the effect of the antagonists, did not favor the hypothesis that imidazoline receptors are involved in the idazoxan-potentiating effect in the rat vas deferens.