Figure 3. Effect of late addition of Ca²⁺ ionophore on the expression of slow MyHCI mRNA.

Cultures were grown for 8 (lane 1), 16 (lane 2), 23 (lane 3), 24 (lane 5) and 29 days (lane 7) in the absence of ionophore. The other lanes represent cultures grown for 22 days without ionophore and thereafter in the presence of Ca²⁺ ionophore A23187 (4 × 10⁻⁷ M) for 1 day (lane 4), 2 days (lane 6) or 7 days (lane 8). Total RNA (20 μg) was isolated from control and ionophore treated cultures at the time points indicated, fractionated on a 1.2 % agarose-formaldehyde gel, and transferred to nitrocellulose. The blots were hybridized with the 3′ terminal ³²P-labelled HinfI fragment of MyHCI cDNA (1 × 10⁶ c.p.m. ml⁻¹) or an rDNA probe from 18S rRNA (1 × 10⁶ c.p.m. ml⁻¹). The positions of 18S rRNA (1.9 kb) and 28S rRNA (4.8 kb) on the ethidium bromide-stained gel are indicated.