Caveolae in ventricular myocytes are required for stretch-dependent conduction slowing.

Mechanical stretch of cardiac muscle modulates action potential propagation velocity, causing potentially arrhythmogenic conduction slowing. The mechanisms by which stretch alters cardiac conduction remain unknown, but previous studies suggest that stretch can affect the conformation of caveolae in myocytes and other cell types. We tested the hypothesis that slowing of action potential conduction due to cardiac myocyte stretch is dependent on caveolae. Cardiac action potential propagation velocities, measured by optical mapping in isolated mouse hearts and in micropatterned mouse cardiomyocyte cultures, decreased reversibly with volume loading or stretch, respectively (by 19±5% and 26±4%). Stretch-dependent conduction slowing was not altered by stretch-activated channel blockade with gadolinium or by GsMTx-4 peptide, but was inhibited when caveolae were disrupted via genetic deletion of caveolin-3 (Cav3 KO) or membrane cholesterol depletion by methyl-β-cyclodextrin. In wild-type mouse hearts, stretch coincided with recruitment of caveolae to the sarcolemma, as observed by electron microscopy. In myocytes from wild-type but not Cav3 KO mice, stretch significantly increased cell membrane capacitance (by 98±64%), electrical time constant (by 285±149%), and lipid recruitment to the bilayer (by 84±39%). Recruitment of caveolae to the sarcolemma during physiologic cardiomyocyte stretch slows ventricular action potential propagation by increasing cell membrane capacitance

‘Death and Axes’: Unexpected Ca2+ Entry Phenologs Predict New Anti-schistosomal Agents

Schistosomiasis is a parasitic flatworm disease that infects 200 million people worldwide. The drug praziquantel (PZQ) is the mainstay therapy but the target of this drug remains ambiguous. While PZQ paralyses and kills parasitic schistosomes, in free-living planarians PZQ caused an unusual axis duplication during regeneration to yield two-headed animals. Here, we show that PZQ activation of a neuronal Ca(2+) channel modulates opposing dopaminergic and serotonergic pathways to regulate ‘head’ structure formation. Surprisingly, compounds with efficacy for either bioaminergic network in planarians also displayed antischistosomal activity, and reciprocally, agents first identified as antischistocidal compounds caused bipolar regeneration in the planarian bioassay. These divergent outcomes (death versus axis duplication) result from the same Ca(2+) entry mechanism, and comprise unexpected Ca(2+) phenologs with meaningful predictive value. Surprisingly, basic research into axis patterning mechanisms provides an unexpected route for discovering novel antischistosomal agents