\documentclass[a4paper,12pt]{article}
\usepackage{array}
\newcolumntype{$}{>{\global\let\currentrowstyle\relax}}
\newcolumntype{^}{>{\currentrowstyle}}
\newcommand{\rowstyle}[1]{\gdef\currentrowstyle{#1}#1\ignorespaces}
\begin{document}

% Put `$' before first column type; put `^' before subsequent ones.
\begin{tabular}{|$l|^l|^l|}   \hline
  \rowstyle{\bfseries}
  Heading & Big and & Bold \\ \hline
  Meek & mild & entry      \\
  Meek & mild & entry      \\
  \rowstyle{\itshape}
  Strange & and & italic   \\
  \rowstyle{\scshape}
  Meek & mild & entry      \\ \hline
\end{tabular}
\end{document}
