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RENAL HEMODYNAMICS AND CARDIORENAL INTEGRATION

Frequency encoding in renal blood flow regulation

¹Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, Rhode Island; ²Department of Physics, Danish Technical University, Lyngby, Denmark; ³Department of Physics, Saratov State University, Saratov, Russia; ⁴Department of Physiology & Biophysics, University of South Florida, Tampa, Florida; and ⁵Department of Medical Physiology, Panum Institut, University of Copenhagen, Copenhagen N, Denmark

Submitted 9 August 2004 ; accepted in final form 19 January 2005

With a model of renal blood flow regulation, we examined consequences of tubuloglomerular feedback (TGF) coupling to the myogenic mechanism via voltage-gated Ca channels. The model reproduces the characteristic oscillations of the two mechanisms and predicts frequency and amplitude modulation of the myogenic oscillation by TGF. Analysis by wavelet transforms of single-nephron blood flow confirms that both amplitude and frequency of the myogenic oscillation are modulated by TGF. We developed a double-wavelet transform technique to estimate modulation frequency. Median value of the ratio of modulation frequency to TGF frequency in measurements from 10 rats was 0.95 for amplitude modulation and 0.97 for frequency modulation, a result consistent with TGF as the modulating signal. The simulation predicted that the modulation was regular, while the experimental data showed much greater variability from one TGF cycle to the next. We used a blood pressure signal recorded by telemetry from a conscious rat as the input to the model. Blood pressure fluctuations induced variability in the modulation records similar to those found in the nephron blood flow results. Frequency and amplitude modulation can provide robust communication between TGF and the myogenic mechanism.

tubuloglomerular feedback; myogenic mechanism; nonlinear interactions; amplitude modulation

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