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Involvement of urinary bladder Connexin43 and the circadian clock in coordination of diurnal micturition rhythm
By H. Negoro, A. Kanematsu, M. Doi, S.O. Suadicani, M. Matsuo, M. Imamura, T. Okinami, N. Nishikawa, T. Oura, S. Matsui, K. Seo, M. Tainaka, S. Urabe, E. Kiyokage, T. Todo, H. Okamura, Y. Tabata, and O. Ogawa.
Nature Communications, Volume 3, 2012, Article number 809
The bladder muscle cells may have a circadian biological rhythm.This study in mice bladders has focused on a possible circadian variation of connexin43 (Cx43), a bladder gap junction protein. The authors have found circadian oscillations of bladder Cx43 and functional capacity in “normal mice”, and compared this with Cry-null mice (dysfunctional biological clock) which did not have this “rhythm”. The authors therefore suggest that bladder “voiding capacity” may vary during the day and night.
Nocturnal enuresis in children and nocturia in the elderly are two highly prevalent clinical conditions characterized by a mismatch between urine production rate in the kidneys and storage in the urinary bladder during the sleep phase. Here we demonstrate, using a novel method for automated recording of mouse micturition, that connexin43, a bladder gap junction protein, is a negative regulator of functional bladder capacity. Bladder connexin43 levels and functional capacity show circadian oscillations in wild-type mice, but such rhythms are completely lost in Cry-null mice having a dysfunctional biological clock. Bladder muscle cells have an internal clock, and show oscillations of connexin43 and gap junction function. A clock regulator, Rev-erbα, upregulates connexin43 transcription as a cofactor of Sp1, using Sp1 cis-elements of the promoter. Therefore, circadian oscillation of connexin43 is associated with the biological clock and contributes to diurnal changes in bladder capacity, which avoids disturbance of sleep by micturition.