Demonstration of functional dipeptide transport with expression of PEPT2 in guinea pig cardiomyocytes

The transporters PEPT1 and PEPT2 accept a broad spectrum of substrates including small, naturally occurring peptides and peptidomimetic drugs. This study aimed to investigate for the first time whether these transporters are expressed and active in isolated cardiomyocytes. PEPT1/ PEPT2 expression in rat kidney (positive control), guinea pig kidney and cardiomyocytes were investigated by reverse transcription polymerase chain reaction. L-Glycyl-L-[¹⁴C] sarcosine (Gly-sar) uptake was characterised using freshly isolated suspensions of adult male guinea pig cardiomyocytes. PEPT2-specific primers recognised mRNA of appropriate size and sequence in cardiomyocytes and kidney, whilst PEPT1 was expressed in the kidney only. The initial uptake (30 s) of 200 μM Gly-sar was dependent on extracellular pH with a maximum at pH 6.0 (237.8±12.2 pmol/ μl) and a minimum at pH 8.0 (72.1±13.4 pmol/μl, 'n'=6± SE, 'p'<0.01, T test). The K'm' and V'max' of Gly-sar uptake at pH 6.0 were 495.5±69.6μM and 1470.5±69.6 pmol μl⁻1 min⁻1. The addition of 10 mM fosinopril, cefadroxil, carnosine, cyclacillin or a variety of L-amino acid containing dipeptides/tripeptides significantly reduced Gly-sar uptake. Gly-sar uptake was not affected by 10 mM D-ala-D-ala, glycine or sarcosine. These results support the presence of a functional dipeptide transporter in isolated cardiomyocytes, with accompanying expression of PEPT2.