In rat ventricular myocytes, PDE3 and PDE4 are the dominant subtypes regulating basal L-type Ca2+ current, while all four PDE subtypes determine the response to cyclic AMP production stimulation.
PDE1-4 subtypes regulate L-type Ca2+ current in rat ventricular myocytes, with PDE3 and PDE4 being dominant under basal conditions.
p-value: p=<0.01
The effects of several phosphodiesterase (PDE) inhibitors on the L-type Ca current (I(Ca)) and intracellular cyclic AMP concentration (cAMPi) were examined in isolated rat ventricular myocytes. The presence of mRNA transcripts encoding for the different cardiac PDE subtypes was confirmed by RT-PCR. IBMX (100 microM), a broad-spectrum PDE inhibitor, increased basal I(Ca) by 120% and cAMPi by 70%, similarly to a saturating concentration of the beta-adrenoceptor agonist isoprenaline (1 microM). However, MIMX (1 microM), a PDE1 inhibitor, EHNA (10 microM), a PDE2 inhibitor, cilostamide (0.1 microM), a PDE3 inhibitor, or Ro20-1724 (0.1 microM), a PDE4 inhibitor, had no effect on basal I(Ca) and little stimulatory effects on cAMPi (20-30%). Each selective PDE inhibitor was then tested in the presence of another inhibitor to examine whether a concomitant inhibition of two PDE subtypes had any effect on I(Ca) or cAMPi. While all combinations tested significantly increased cAMPi (40-50%), only cilostamide (0.1 microM)+ Ro20-1724 (0.1 microM) produced a significant stimulation of I(Ca) (50%). Addition of EHNA (10 microM) to this mix increased I(Ca) to 110% and cAMPi to 70% above basal, i.e. to similar levels as obtained with IBMX (100 microM) or isoprenaline (1 microM). When tested on top of a sub-maximal concentration of isoprenaline (1 nM), which increased I(Ca) by (approximately 40% and had negligible effect on cAMPi, each selective PDE inhibitor induced a clear stimulation of cAMPi and an additional increase in I(Ca). Maximal effects on I(Ca) were approximately 8% for MIMX (3 microM), approximately 20% for EHNA (1-3 microM), approximately 30% for cilostamide (0.3-1 microM) and approximately 50% for Ro20-1724 (0.1 microM). Our results demonstrate that PDE1-4 subtypes regulate I(Ca) in rat ventricular myocytes. While PDE3 and PDE4 are the dominant PDE subtypes involved in the regulation of basal I(Ca), all four PDE subtypes determine the response of I(Ca) to a stimulus activating cyclic AMP production, with the rank order of potency PDE4>PDE3>PDE2>PDE1.
Verde et al. (Sat,) conducted a other in Healthy (rat ventricular myocytes). Phosphodiesterase (PDE) inhibitors (IBMX, MIMX, EHNA, cilostamide, Ro 20-1724) vs. Control (basal conditions or isoprenaline alone) was evaluated on L-type Ca2+ current (ICa) amplitude (p=<0.01). In rat ventricular myocytes, PDE3 and PDE4 are the dominant subtypes regulating basal L-type Ca2+ current, while all four PDE subtypes determine the response to cyclic AMP production stimulation.