title: T-type (alpha1G) low voltage-activated calcium channel interactions with nitric oxide-cyclic guanosine monophosphate pathway and regulation of calcium homeostasis in human cavernosal cells.
abstract: BACKGROUND
  Nitric oxide-cyclic guanosine monophosphate (NO-cGMP)-mediated relaxation of cavernosal smooth muscle during erection is accompanied by a decrease in intracellular calcium concentrations ([Ca2+](i)). However, it is not known whether and how an increase in [Ca2+](i) is responsible for (i) initiating smooth muscle contraction/detumescence following relaxation; and (ii) maintaining the penis in a flaccid state under nonstimulating conditions.
  
  
  OBJECTIVE
  To elucidate (i) the mechanism(s) of [Ca2+](i) homeostasis regulation in human cavernosal smooth muscle cells (HCSMC); and (ii) how NO-cGMP interacts with such [Ca2+](i) homeostasis.
  
  
  METHODS
  We evaluated the expression and function of both T-type and L-type Ca2+ channels in HCSMC by employing selective probes/inhibitors using various cellular and molecular techniques (e.g., reverse transcriptase and real-time polymerase chain reaction, cell proliferation assay, fura-2 Ca2+ fluorescence spectroscopy, enzyme-linked immuno-absorbent assay (ELISA)).
  
  
  METHODS
  We have demonstrated for the first time significant interactions of NO-cGMP with the T-type (alpha1G) Ca2+ channel in HCSMC.
  
  
  RESULTS
  Our results suggest that in addition to NO-induced rapid and transient decrease in [Ca2+](i) that results in smooth muscle relaxation, NO-cGMP also enhanced mRNA expression of the T-type (alpha1G) Ca2+ channel resulting in delayed elevation of [Ca2+](i). This could be abolished by a selective T-channel blocker, NNC 55-0396. Another unique finding of this study is that dose-dependent HCSMC proliferation in vitro by NO is associated with the activation of the T-type (alpha1G) Ca2+ channel that regulates [Ca2+](i) homeostasis in these cells.
  
  
  CONCLUSIONS
  Human cavernosal cells express T-type (alpha1G) Ca2+ channels that are involved in maintaining [Ca2+](i) homeostasis and regulation of NO-cGMP-induced smooth muscle relaxation-contraction responsible for penile erection, flaccidity, and tonicity. Targeting these Ca2+ channels may (i) associate various comorbidities with the onset of erectile dysfunction; (ii) provide a biochemical basis for differences between therapeutic profiles of various phosphodiesterase type 5 inhibitors, especially in nonresponders to current therapy; and (iii) provide biochemical basis in understanding mechanism(s) of drug tolerance.
authors.affiliation: Department of Urology, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112, USA.
authors.forename: Xiangbin
authors.initials: X
authors.lastname: Zeng
authors.forename: Brian
authors.initials: B
authors.lastname: Keyser
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.forename: Suresh C
authors.initials: SC
authors.lastname: Sikka
mesh_terms: D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D020747:Calcium Channels, T-Type / Q000235:genetics / Q000378:metabolism*; D018929:Cell Culture Techniques; D006152:Cyclic GMP / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008297:Male; D009126:Muscle Relaxation / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology* / Q000378:metabolism*; D009569:Nitric Oxide / Q000235:genetics / Q000378:metabolism*; D010413:Penis / Q000166:cytology* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics*; D013050:Spectrometry, Fluorescence; D015854:Up-Regulation / Q000235:genetics / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D020747:Calcium Channels, T-Type; D017931:DNA Primers; D018076:DNA, Complementary; D012333:RNA, Messenger; D009569:Nitric Oxide; D006152:Cyclic GMP; D002118:Calcium